The most common forms of energy you'll meet in school are kinetic, potential and elastic energy.
Kinetic energy solely depends on the mass and speed of a body. So, as long as a body is not still, it has kinetic energy. The formula to compute the kinetic energy of an object is
Potential energy depends on where we put the origin for heights. So, you arbitrarily set a certain height to be 0 (for example, the floor of the room you're in or the ground, if you're in the open), and then you compute the height of a certain object with respect to the origin you just set. For example, if I set the height origin on the floor of my house, an object on a table will have height = 1 meters. But since I live on the 4th floor of a flat, if you set the origin on the ground outside, the same object will be several meters higher!
The formula to compute the potential energy of an object is
where g is the gravity acceleration, m is the mass of the object and h is its height.
Finally, elastic energy is accumulated every time you compress an elastic object. That object becomes ready to release the compression, and so it stores energy which is about to be unleashed. For example, if you compress a spring and force it to stay compressed, and then put a little ball at the end of the spring, the ball is not moving yet, but as long as you release the spring, it will push the ball forward. Obviously, the more the spring is compressed and/or the stiffer the spring was, the greater push the ball will receive. The formula to compute the elastic energy of an object is
Where k is the stiffness constant of the spring, and x is the measurement of how much it was compressed.