You have to feed them a variety of foods, and keep the female in a tank next to the male. After a few weeks, the male will build a bubble nest ( a bunch of bubbles at the surface of the water ) and the female can be added.
Usually, you don't leave the female in for longer than a day. After that you take the female out, and the male betta will care for the babies. they will fall from the next, and he will scoop them up and put them back into the bubble nest.
once the betta babies are free-swimming, the daddy should be removed from the tank.
the bettas will spawn more than 100 fry.. usually, so you need to be prepared to home each of them, also to be able to separate the male babies once they are aggressive.
the babies should be fed several different LIVE foods.
breeding these bettas really shouldn't be something you do on a whim. there are so many petstore bettas, you wont be able to home most of them
your bettas should be in heated tanks, not little cups. please do research on the fish before you try sticking two aggressive fish into one small, most likely cold tank to get babies.
if you do your research think about buying a quality pair on aquabid.com
also if you don't know what cycling is please do not breed fish until you understand the basic things.
ok good luck with that