Here's a breakdown:

* Nebula: A vast cloud of gas and dust in space. They come in various shapes and sizes, and some glow brightly while others are dark and dusty.

* Star Formation: Within a nebula, gravity can pull the gas and dust together. As the cloud collapses, it heats up, and eventually, the core becomes hot and dense enough to trigger nuclear fusion. This process marks the birth of a star.

So, you're describing the process of star formation, which begins with a nebula.