To begin and understand what energy manipulation is, you have to understand that everyone who can use magic even slightly used energy manipulation for their spell. How did they use energy manipulation for their spell is something you may ask. Magic is the use of energy combined with intent and focus. When you cast a spell you generally direct where you want your energy to go depending on the spell cast.
Energy manipulation or EM is the Direct manipulation of energy, the psi ball for example is EM exercise. A fact that you may not know, when you practice various EM exercises, you work on your control over your own energy.
How is control important?
Whenever you cast spells for one reason or another, you use energy, having better control means less energy is wasted into the spell. Lets say normally you pour so much energy into your spell doesnt work or works correctly. When you learn to manage your energy better, You should be able to cast spells without exhausting yourself mentally, physically, emotionally. You do exhaust yourself due to over focusing on that one thing. So not only does control help you use spells and not waste energy, it also makes it so you're not as exhausted from using spells.
What are the requirements for learning energy manipulation. Well the biggest thing you need is the ability to focus your mind on your energy, Meditation should help with that. The next requirement is determination and the ability to draw onto your energy or the energy around you.
How to draw upon energy
To draw upon your energy, you really need to visualize your energy in a central area(stomach, near the heart, ect). Visualize a pull on that energy and pull it in the direction and or path you want to, once the energy is gathered in an area, you may feel a strong sensation in that area. You want to draw the energy to your fingertips and then out to be released. You can try to gather energy there and create things such as a psi ball for control, you can go beyond the psi ball exercise to help work on control a bit more.
Types of energy
You may have heard of there being different types of energy, Does that mean that there are separate individual forms of energy. If so, than its a lie. "types" of energy are nothing more really than using energy with an imposed thought. For example, if you use"healing energy", your generally thinking about healing someone. You think about harming someone, you generally would gain dark energy. Now converting the "type" of energy from one kind another is pretty simple, you need to have a "type" and bring it to neutral or energy without thought, emotion, idea, ect. You then impose your new thought, or emotion on the energy used to convert to another "type".