Construct
A Construct is a fabricated spiritual servitor. They are sometimes called egregores or elementaries in other systems of classification. They can be made in any form for virtually any purpose. You can make them as smart or stupid, fast or slow, as you need. You are GOD to a construct that you have created.

Things to remember
ALWAYS give your construct a time limit to exist in that form. After that time limit is up, the energies should be returned to where they came from (program it in- simply intending to have this happen should do it). If you don't provide a time limit, a construct can have a tendency to develop a mind of its own and get out of control, especially if left on its own and forgotten. Never forget to provide a time limit. 6 months-1 year is fine for most. Up to 5 years is acceptable for long-term applications.

Constructs tend to act according to the form you give them; if it is made to look like a tiger, it will tend to act a bit like one. You can be creative. If you're making something to protect someone, be sure to give it something to defend itself with; claws, teeth, guns etc. Borrow ideas from science-fiction if you wish. Your imagination is the limit. Your skills will follow with sufficient practice.

How to make a Construct
First, plan out all the information for it; everything you want it to be able to do, how it will look etc. Write all this information down on a piece of paper (or in your personal journal) if you wish so you may keep track of it. Then, while you're creating the construct, you can read off all of the features and specifications like a recipe if necessary.

Prepare yourself for the creation process by shifting mental gears with meditation or just general relaxing. You need to be completely focused and ready when you commence any operation.
Then, draw in energy, one type at a time (if you work that way), and concentrate/direct it in accordance with your Will. Just imagine strongly that you're sucking in energy (in whatever phase you need) and breathing it out into an area in front of you where you mold it into the shape you want it; use your hands if you need to at first. Visualize strongly the thing that you're creating, right in front of you. You almost paint the energy where you want it. Push or exhale the energy out of your hands or mind if you must. You might build a construct in sections starting first with one phase of energy (applying it according to its properties), then continuing on with energy in another phase, and then another, until you have completed the task of building one construct. There are many ways to view the process.
Once you have finished making your construct look the way you want with all the features on it you need, then it is time to program it. Imagine that a construct is sort of like a living astral robot that you have created. Now, you must program it so that it can carry out your tasks. All you need to do at this point is to imagine that you are consciously injecting information into it and programming it. If it assists you to do so, you may pretend you are 'breathing' information into the construct; just formulate the program/mental command in your head, and then exhale it into the construct (almost expelling it like in an orgasm from your mind or body- doesn't need to be as intense though). A simple set of mental commands should be sufficient. Things like, "Your job is to protect so-and-so," and, "you are intelligent and know what I wish you to know about the job you are to perform," are usually fine at first. Your first attempts at constructs will likely be simple. As your skills improve, the set of mental commands used to program one with will probably become more complicated. Pay meticulous attention to detail and you'll do fine. As always, your Will or Intention WHILE you are building and programming the construct is what determines how good of a job you do.

Don't forget the time limit! Just put that in as part of your construct's programming. Note: some find it useful to assign names to their creations so that they can be called back to report on progress, or just simply return home. This could also be a useful practice to increase the amount of control you have over a construct. Most people don't give out the names of their constructs without a good reason. It may be a good idea to program yours not to respond to the commands of anyone except you, unless you're making it to assist someone.

Once you've finished creating and programming your construct, dismiss it to perform its task and have confidence that all will go as you've planned.

Don't think of failure while doing anything; such thoughts detract from your effort and scatter the force of your intent. Developing the mindset that failure is not an option and doubts are not possible whenever you commence an operation may be beneficial in keeping your focus; sort of like shifting gears in your mind beforehand everytime. I used to build a construct first then program it for the task I wanted it to perform, but you may find it easier to program it while you build it. When I create them now, they seem to spring into life without much effort, being created and programmed simultaneously. With practice, everything is always easier. The more work you put into it, the better it will be. Over time, you'll develop your own style.

Depending on your personal skills, you may or may not perceive your creation visually. It might be that you only feel its presence. This is normal.
 

Additional Notes
For most people, it isn't always a good idea to try to add to a construct or change it after you make it. It can tend to screw them up if you're not careful. Generally, if you know what you're doing you can get away with it. I've never consciously added to anything. They always seem to be under my conscious control whenever I want them to be. This may not be true for all people, especially at first.

If you prefer to work with energy in the elemental phases then it is good practice to use at least 2 elements for better stability when making a construct. Remember that each element (energy in that phase) has a different function, or tends to respond differently while in that phase. Use them accordingly for best results with those methods. Otherwise, just draw in spiritual/pranic/or psychic energy (whatever you want to call it) and use it in accordance with your will.

Should you decide that a construct of yours is no longer useful prior to its termination period, you may simply return the energies used to create it to their point of origin. You are God to a construct that you have created. This is your right as a creator. I tend to disagree with some magickians who believe that once you create something it's permanent and hard to destroy. I've personally had no problems disassembling anything I've ever made, although the mental program for making it is still in my consciousness, and certainly still exists in essence within the Unmanifest...but then the essence for all things is in the Unmanifest to begin with.

If you borrow personal energy from another spirit or person (with their consent), or if you make something in conjunction with someone else, that person or spirit usually has access to the thing you made, and can destroy it if they don't like what you did with it.

As was previously mentioned, you are God to a construct that you've created. Because of this, you will also be held responsible for your creations. If something you make causes trouble, who/whatever the construct angered will eventually come looking for its creator. Might be a good idea to keep that in mind...

Thought-forms
It should be mentioned that there are things similar to constructs known as Thought-forms. Thought-forms can be made to perform the same tasks as constructs, though there is a major difference in their creation:

A thought-form is created from your personal energy, and is thus an extension of your consciousness. It is part of you.

Constructs are made from imported energy, and although they have a link to you, they are not part of you. If you made a thought-form (for example, in the form of a lion) to attack someone/something, and your thought-form was destroyed, YOU WOULD FEEL IT. It would be highly unpleasant. However, if a construct of yours was destroyed, you would feel nothing though you would probably be aware.

It is not a good idea to create too many thought-forms at once. By doing so you risk spreading your consciousness too thinly (because you're dividing up parts of yourself), and there is always the chance that one of them could have more consciousness than the main part of you should you get too carried away (and then you're screwed). To get rid of a thought-form that you've created, simply re-absorb it back into yourself. Just Will it so, or intend it and use the imagination as a tool to do it. I have read and heard accounts of a person's negative energies or emotions toward someone/something coalescing into a harmful thought-form and attacking the individual and/or other people. If this should happen, the procedure is the same; re-absorption by the individual who created it. Though because of the nature of this particular kind of creation, one must be aware that upon re-absorption the individual will experience exactly the same negative emotions he/she was having when the thought-form came into being. The emotions and inner-conflicts that caused the creation of the thought-form must consequently be resolved and worked through to avoid a recurrence. This entire procedure can be dangerous and unpleasant, but is necessary if your thought-forms get out of control. Only the most advanced adept should ever try to absorb another person's negative thought-form; even then, he/she will have to undergo a period of purification and balancing afterward.

Something to think about: In some cases, those diagnosed as insane are often plagued by their own uncontrollable thought-forms in the form of hallucinations. A skilled magickian may be able to perceive and destroy them for the individual, but unless the source of the illness is found, the person would unconsciously create more.