Protostars are the early stages of star formation, occurring when a dense region within a molecular cloud collapses under its own gravity. As the material gathers, it heats up, forming a hot core surrounded by a rotating disk of gas and dust. This process can take millions of years, and during this time, the protostar continues to accumulate mass from its surroundings. Eventually, when the core temperature becomes high enough, nuclear fusion ignites, marking the transition from a protostar to a main-sequence star. This is a crucial phase in the life cycle of stars, influencing their eventual size, brightness, and lifespan.