What stage comes after the birth of a star?
The main sequence stage, where stars fuse hydrogen atoms into helium.
Once a star ignites and begins fusing, it will start to dim and settle onto the main sequence. Every star spends the majority of its life as a main sequence star, because the star is mostly hydrogen, and because hydrogen fusion takes place at the slowest rate.
The amount of time that a star spends fusing hydrogen depends on the stars mass. For a yellow dwarf star like our Sun, this stage will last 8-10 billion years. For more massive stars, hydrogen fusion may take place for 10-100 million years, and for red dwarf stars, which are smaller than the Sun, the stars entire life of tens of billions of years will be spent fusing only hydrogen.
For stars like our sun and larger, when they run out of hydrogen, they will enter the giant stage and move off of the main sequence. This stage will be much shorter, and the star will eventually die as either a supernova or a planetary nebula.