Answer: The asteroid belt lies between the orbit of Mars and Jupiter i.e between the inner planets and the outer planets. It was believed that when our solar system was being formed, a dwarf planet eventually started to form between Mars and Jupiter. But due to the presence of Jupiter's strong gravitational force, the materials were not able to form a planet and kept revolving around the planet Jupiter in an orbit.
The asteroids ranges in size from a few meters to a hundreds of kilometers and moves at a speed of about 80000-85000 km/hr. There is continuous collision between the asteroids and some of them sometimes enters earth's orbit.