I didn't see anyone mention this. You can only have one male betta in a tank. If you have 2, they fight. You can have as many females in the tank as you like, with or without one male. Usually the males have the flashy tails, and the males are the ones sold in those little plastic cups. The females are community fish, so they will be in a tank together, possibly with other fish.

I never had a female. I have kept several males - one at a time - in my tank with other fish. Only once I brought one home and he started attacking the tetras. Back he went next day.

They really are wonderful to watch, it is SO relaxing!