Planet formation begins in a solar nebula, a large cloud of gas and dust in space. Over time, gravity causes this material to clump together, forming larger bodies called planetesimals. These planetesimals collide and merge, gradually building up to form protoplanets. As protoplanets grow, they continue to attract more material through gravity. Eventually, some of these protoplanets become large enough to clear their orbits, leading to the formation of planets. This process can take millions of years and results in the diverse range of planets we see in our solar system today.