I don't tend to use a lot of tools. Part of the reason for this is that I've found that unless I keep a "toolkit" handy at all times, the time I really need the kit will invariably be a time when it's not handy. I just don't trust my luck on those things, so I've learned to do what I can mostly without tools. Sometimes however you wish you had a tool - perhaps you need an athame to cut an energy line or something similar. In those situations I just go ahead and make one out of what I call thoughtform energy. The term really says it all - its the energy you use to give form to something you think up, to put it a bit inelegantly.
Thoughtform energy can be used for a whole lot of things. You can make tools out of it, you can build rooms out of it, you can even make semi-spirits out of it - and yes I did imply you can make "external intelligences" out of it. And actually that's the stickiest point of this whole subject. Thoughtform spirits.
What are they? In simple terms they're spirits you make so serve a purpose at a time. Perhaps you create a spirit via your visualization of an angel. Perhaps you make an "imaginary friend" for company. But the spirit ultimately comes from you. Why is this so tricky? For two major reasons - number one, how you treat that spirit, and number two - what if you don't know you made that spirit?
The first question is a sticky ethical question. Is a construct entitled to the same rights as a spirit? I generally think so, for two reasons. First, if you treat your construct with a lack of respect and attention, you will quickly undermine your creation and "unmake" it. Second, if a construct is shared with others, suddenly you're not the only one feeding that construct, and it may not be as dependent on you as you'd like. That construct can get ideas of its own if it's fed enough energy from other people; it's simply no longer just your creation, but is a collective creation. Who knows that it may not become independent of you, and suddenly one day you need to petition it for something? For this reason, working with constructs can be very tricky, and respect should be a cornerstone of all work.
Just as an example of this kind of activity - a friend told me once a story about a circle she was part of. Having the sense of humor they had, they decided to try an experiment, and as a group poured all the energy they could into the worship of the great and all-powerful... Tweety-Bird. As my friend related to me, one day she got a call from a friend of hers, who was a member of a different circle. And the friend imparted to her the bewildering experience her circle had when out of nowhere this tweety bird flew though the circle...
Generally anything you pour enough energy into will come to life somehow. That's why it's a darned good idea to keep an eye on yourself, and what you pour energy into. I don't watch horror movies anymore, for example. Why? Because I'm sick of having to deal with the thoughtforms generated if I pay too close attention to the movie and not enough to myself...
The other question mentioned above comes exactly from this point - what if you don't realize you made a spirit? This question comes into play a great deal in the pagan community (that I can see), and manifests itself most often in what I call Psychic War Syndrome (Or PsiWar Syndrome). Ever see a group of new occultists out "saving the world" every weekend when the rest of the world doesn't even notice what's going on? Generally what's happening there is that someone generated, out of thoughtform energy, a perceived enemy which they now need to thwart. Often this occurs when someone wants to stretch their wings on their skills, or if they just want to feel special. So the subconscious (which is more often than not trained to make stuff by this point, but lacks discipline) responds to that need by generating a monster. And the beast is ever so hard to kill - because it modifies itself based on what you try, and if you really really think this'll work it works (because you told the monster it would work), whereas if you doubt it'll work (or think it'd be way too easy) it won't.
And let me say right now - just because a beast is made of thoughtform energy does not make it harmless to the circle dealing with it or its maker. If anything it is more harmful because it is part of that person, and unless the person thinks to shield himself from himself, he often suddenly finds he can't defend against it. And surprise surprise - it is intimately familiar with that person's dark side, and knows just which buttons to push. Just because a person makes a monster from himself (generally not realizing it) doesn't prevent that monster from causing its maker to make stupid mistakes and potentially harm himself. Worse, that monster could expose an unready person to his own weaknesses, fears, and basically his dark side - which can be an extreme psychological trauma.
So thoughtform energy is really a double edged sword. It can be one of the most versatile and useful tools in your armory, but it can also be a threat. However, and in my experience, the better you know yourself the less likely you are to use it unwittingly, so extensive use of this tool should probably be accompanied by some massive soul-searching and working. It's certainly something I couldn't do without.