Are rocks made of asteroids and how?

Answer 1

The material that forms rocks ultimately does come from asteroids. But the rocks on earth have been destroyed, re-formed, and altered numerous times by geologic processes, so it would be erroneous to say they are "made of asteroids."

As to how:

The planets originated from a disk of gas and dust orbiting the young sun. The dust coalesced into larger particles, which eventually grew into asteroids. These asteroids collided with one another, forming larger and larger bodies. Some of these became planet-like objects called planetesimals, which collided to form proto-planets. Eight of these proto-planets eventually became the planets we know today, including Earth.