As the clouds became more and more dense, they became hotter because of the collisions of the hydrogen atoms. The clouds were so massive that they began to collapse in on themselves as well, creating more heat. There were more and more collisions until these clouds lit up and began to shine. At the center of these clouds, where the concentration of hydrogen was the greatest, stars began to form and light up the void in which they were in.
The fuel for these stars was of course hydrogen. They burned this fuel into helium in the form of fusion reactions. The stars had different life spans, depending on their mass, and all at some point or another died; some in the form of a supernova and some in the form of calm and peaceful deaths. In either case, the stars ejected their materials into space and thereby provided the foundation for more generations of stars, solar systems, and planets. All of this occurred due to the accumulation of hydrogen in the form of “clouds.”