Here's a breakdown of the process:

1. Giant Molecular Cloud: A large cloud of gas and dust in space starts collapsing under its own gravity.

2. Protostar Formation: As the cloud collapses, the material at the center gets denser and hotter. This hot, dense core is a protostar.

3. Nuclear Fusion: Eventually, the temperature and pressure at the core become so high that nuclear fusion begins. This is when hydrogen atoms fuse to form helium, releasing enormous amounts of energy.

4. Star Birth: The protostar becomes a true star when nuclear fusion becomes the dominant source of energy, and it starts to shine brightly.

So, a protostar is essentially a baby star still undergoing the process of formation.