This is for beginners, however all are welcome read it.
There are many types of magick that exist, but people from nearly every path agree that there is one thing that ties the working of all the different types together; the force of Will. Whether you're casting a simple spell, or summoning spirits, the most important thing to have is a Will as strong as you possibly can.
 What is Will and why is it important?
Will, or Willpower, is an aspect of the human psyche that can be thought of as the strength of ones ability to affect the world around them, in magickal ways or otherwise. A good metaphor for it would be to say that it is your "magick-muscle." If every spell is a crate, then Will is what you move it with, and the strength of Will determines how far you can move it.
In magickal practices, Willpower is key. It is what allows a spell to be realized. A common mistake that beginners make is confusing Will with Want, and the two are very different. If you have the Will to make a spell work, you also probably have the want for it to work; however, just because you have the want of something, doesn't mean you have the Will to get it. Want must be powered by Will if you are to achieve your goals.
 Willpower vs. World
In the first segment, Will is defined as "...the strength of ones ability to affect the world around them, in magickal ways or otherwise." Now, while it is important to develope one's Will, it is a huge folly to think that your Will can ever become an "ultimate" force, or a force that exists outside the laws of nature. Just as you have your own Will, so does every other living thing on Earth, and so do the spirits that exist. It is inevitable that your own Will shall clash with the Will of another, then. In such a case, it usually the stronger Will that prevails. When dealing with spirits, in a manner that is unpracticed and not sanctioned, it is more often that a spirit will prevail in matters of Will. Since they do not have a physical body and are composed entirely of energy, their Will is usually more practiced than ours, as that is how they influence the world at all times, while we rely on our physical bodies for much of that work.
Our Will cannot defy the laws of nature for several reasons, depending on different beliefs. I'll explain the one that I accept. As I used as a metaphor earlier, Will is the "magick-muscle" and like any muscle, grows bigger and stronger with exercise- however, this muscle works differently than the ones in your body. It is used to influence the subtle world, which can in fact affect the physical world-that is magick- but humans' Wills are almost never strong enough to affect it in a way that would be, for example, throwing a cup across a room. Or even something much smaller, like floating a feather into the air.
It has been documented by some sources that persons possessed by "demons" have caused objects to fly through the air, so you might then wonder why you cannot do the same. The answer is this: "demons" are spirits, and therefore use their Will for literally everything they do. That's a lot of exercise, right? On top of that, they've been using their Will for everything for hundreds, thousands, perhaps billions of years. Think about that; now think about you. You've probably been using your Will to perform magick for less than 70 years, and unless you are in a constant state of energy working, you only use it part time. That would be the equivalent of a 5 year old child standing next to an Olympic body-builder, or some such thing.
Even if you were to have the strongest of Wills among humans, you can't change reality for reasons related to energy, which I'll explain in another post that I may or may not write.
 Will + Some
Will is, obviously, not the only thing that goes towards powering magick, however I'll try to keep the talk about them to a minimum as this post is only about one. There are a few other thing that all influence eachother, and unless they are balanced properly, they're basically useless when it comes to performing magick. These things are Energy, Will, and Belief.
-Energy is what constitutes a spell, and all subtle things.
When you have amassed only Energy, probably not much will happen. It's like having a bunch of wax and not making anything from it.
-Will is (see section 1).
When you have only your Will, you probably won't be able to perform a working spell because you have no Energy or Belief that a spell would work.
-Belief is the faith that what you're doing will work.
Belief is almost useless when trying to work magick unless you have Will to power it and Energy to construct it. Believing you can do something and doing it are different.
So while you may have a Will of iron, it doesn't always mean your spell will be successful.
There is one major pitfall to avoid, it is Want.
Want is different from Will in the fact that Want is when a person wants something to be given to them, where Will is reaching out and grabbing it. If you are practicing Want, it might happen that a spirit or person gives you your desire. Do not mistake this as you influencing the world with Will, it is urging others to act to your advantage. Want can also lead to delusions that you are performing magick when you are not, or that impossible things are possible.
I hope you've taken something useful from reading this, and I'd just like to state that everything written is based around my personal beliefs and I, in no way, mean to say that other beliefs are incorrect.
I might write other articles on Energy and Belief, also for beginners, but I'm not sure if or when I'll do them. If you read this and have further questions, feel free to mail me and I will answer them to the best of my ability.
May every blessing attend you ^^