Question: how many different types of stars are there?

Edward Bovill answered on 20 Mar 2013:

Most stars are currently classified by their temperature and how bright they are in a system called the MKK system.
The letters O, B, A, F, G, K, and M, are given to indicate how hot they are, where O stars are the hottest and M class stars are the coolest.
The hottest stars (O class) are so hot they shine blue, and as you get cooler the star looks white (A), then yellow (G), orange (K) and finally red (M).

The Roman numerals 0, Ia, Ib, IIa, IIb all the way up to VI and VII are given to show how bright the stars are.

0 class stars are really, really huge stars called hypergiants and shine incredibly brightly.
VII stars are called white dwarfs and are really small stars that don’t shine brightly at all.

Our Sun is a class G2V star and is technically a yellow dwarf star as it is really quite small compared to other stars in the universe.