What is a nebula? How does it form a protostar?
A nebula is a cloud of gas and dust which can be millions of light years in diameter
Protostars are formed when the gas and dust in a nebula start condensing. Its gravitational force increases as its mass increases causing more and more condensation.This leads to formation of a pre main sequence star in which nuclear fusion starts.
Then it matures into a main sequence star which has different outcomes based on the mass of the star