1. Definition of ‘On’ is-One thing is covering the other. Generally, it touches the other object or its surface. Also, it can a part of the surface in some scenarios. For instance, putting paste to the brush.
Ex - Write it down on a piece of paper. / Sit on the chair.

2. On is used when one thing covers another or lays on the top of it. Although, this definition matches the definition of On and On often replaces over when it’s used to convey ‘on top of.’
Ex - The plane flies over the sea. / Put the cream over the cake.

3. Above is usually used when you want to say that something is higher than another object. It also hints of a certain position.
Ex - The temple is above the hill. / The king sits above the rest of his courtiers.