If you have a male that is blowing bubbles and has a bubble nest (group of bubbles stuck together on the surface) then put the female's bowl next to the males for a few days. He will see her and start displaying to her. In a couple of days you can put her in his tank and see how they go. Monitor them closely because some males will kill females.
If the male does not have a bubble nest then make sure you don't have too much surface turbulence in his tank. Male Bettas need fairly calm water for their nest to stay together.
If the male likes her and she is ready to breed, they will swim side by side and she will lay a few eggs at a time. The male will fertilise the eggs and then pick up each egg and coat it in a bubble, and then put the egg in his bubble nest. This continues until the female has expelled all her eggs and then the male will chase her away. You need to monitor them closely at this stage because males regularly kill females after breeding. When they have finished breeding the female will usually hide and you need to scoop her out and put her back in her own bowl.
The male will care for the eggs and fry during the first few weeks of their life.
If they do breed and the eggs hatch, you want to cover most of the tank with some sort of cover to increase humidity and keep the surface and air warm for the fry.
------------------------
The females have a white ovipositor (egg laying tube), which is a little tube that sticks out under her belly.
Female fish develop eggs when they are in good conditions, good water, correct temperature and lots of food. They don't re-absorb eggs because a male fish could come along any time to breed with. Unfortunately in an aquarium, female fish can become egg bound if a male is not available to breed with. This is common in Danios and tetras but does sometimes happen in Bettas, altho not nearly as often.
