Core temperature needs to be 10 million K, kicks off the proton-proton chain. The energy from the nuclear fusion creates enough thermal pressure that gravitational collapse is halted. Now have gravitational equilibrium with balance between gravity and thermal pressure. The star is now a main-sequence star . Like everything else about a star, the time to get to the main sequence from the initial formation of the protostar depends on the mass.
Bigger stars form more quickly.
We look at how a star evolves by looking at how its temperature and luminosity change as it gets older. Like the H-R diagram but rather than plotting how the star looks now, we plot its lifeline or evolutionary track. Basically similar but some differences in tracks, again tied to mass. Can look at a massive-star forming region like the Orion nebula and see the different masses of stars forming and build up the evolutionary tracks. Stars never form by themselves.