One simple physical concept lies behind the formation of stars: Gravitational instability. The concept is not new. Newton first perceived it late in 17th century.

Imagine a Uniform, static cloud of gas in space. Imagine then that the gas is somehow disturbed so that one small spherical region becomes a little denser than the gas around it so that the small regions gravitation field becomes slightly stronger. It now attracts more matter to it and its gravity increases further, causing it begin contract. As it contract, its density increases, which increases its gravity even more soit picks up even matter and contracts even further. The process continues until the small region of gas finally forms gravitationally bound object