Usually, male and female Bettas should be kept seperatly unless you are trying to breed, but that needs to be done very carefully, you can't just put them together or they will fight.
I don't have any female Bettas myself but there are a few members on here who do and I'm sure they can offer you some more advise. There have been a few threads about keeping female bettas recently, maybe do a keyword search of the forum too?
My understanding is that female bettas should either be kept on their own or in groups of 3-5 minimum to prevent fighting. How big is the tank you are going to use?
If you just wanted to keep a single female betta, you may be able to keep her with your single male using a divder and making sure the environment is right for them both, depending on the tank size again. I think I have heard of that before. Somebody else will need to confirm that, because I'm not completely sure. Or you can keep a single female betta quite happily in her own tank