The basic idea is that it is pulled together by its own gravity. For more details, check the Wikipedia article on "protostar".
A prostar is sometimes refered to as a young star. It is a star early in its formation created in a nebula. What a prostar will do is develop into a star you know, such as main-sequence stars, supergiants, or dwarfs. It all depends on the mass of the star on what it will form into.
The first stage in a star's life is as a nebula. As the gravitational forces spin faster, the star enters it's second stage, that of a prostar.
a nebula is one nebula. nebulae are 2 or more nebulas.
it is not the it is a stellar nebula considering that there are multiple stellar nebulas in the universe. what a steller nebula is though is dust and such maing a nebula then when the nebula is strong enough to make a star is creates a prostar, then it is either a massive star or a non massive star. soon they will either turn into a super giant or a red giant. then either the star will explode or simply poof then either it is a white dwarf a neutron star or a black hole. the end
a planetary nebula forms after a hsb o3iii
Emission nebula glow and reflection nebula reflect the light form other stars
Yes. Stars form within a nebula.
If the nebula is gravitationally unstable, it collapsing & forming stars!
protostar or nebula
An explosion from outside the nebula
A nebula may condense and ignite to become a star, conversely a star may explode and form a nebula.
Dust and particles.