What are protoplanetary bodies and what do they do?
A protoplanetary body is a clump of material which will combine with others to form a planet, can be said as birth of a planet.
A planet forms from a protoplanetary disc which is a disc of material orbiting a star. The dust and ices in the disc collide and combine to form protoplanetary bodies. These in turn collide and combine to form bigger bodies.
Ultimately where will be just one body in the orbit which is the newly formed planet. Some protoplanetary bodies may combine to form moons of the planet.
One of the definitions of a planet is that it has cleared its orbit of other bodies. This is one of the reasons why Pluto lost its planet status.