Question

How does a star form from a nebula?

Answer 1

The nebula collapse into themselves, producing protostars, which in turn will become main sequence stars.

Explanation:

First, I need to clarify that stars can only form in certain types of nebula: Reflective, and Dark (both are interstellar clouds of gas and dust). Star formation begins when the denser parts of the cloud collapse under their own weight or weak gravity. The form cores of dust/gas, usually 10^4 solar masses. The cores now denser than the outer cloud, so they collapse first (again).

As the cores collapse, they form clumps, which then form into protostars. This process takes about 10 million years. The protostars will eventually turn into stars.