You cannot just buy two bettas and place them in a tank hoping to breed them. As with all fish, they need to feel comfortable and be heatlhy. As suggested, keep the fish seperated for now.
The bigegst concern is getting the female ready to breed. To get both "parents" ready, have the temperature around 80 degrees constantly, and have the water level dropped in each tank a few inches for at least 3-4 weeks. Feed them very well (blood worms, pellets, etc) for the weeks. The female should begin showing vetical bars, whcih means she is ready to breed. This is where you can start.
Divide the male's tank in half, with him on one side. Dont run a filter, or if you do, a sponge-filter set very low. Adding live plants helps as well. The water level should be around 3", no more than 5". The male should have a bubble nest as well.
Add the female to the other side. If she wants to breed, she will try to get over to the male, flare a bit, and show the vertical bars. After a certian time period, take the divider out. The male and female should chase each other for a bit, and then intertwine. The female will release the eggs, and the male will bring it up to his bubble nest. This will go on for anywhere from 10-60 minutes, sometimes more. After they are done, remove the female.
The male will protect the eggs and place them in the nest when they fall out. When they hatch, he will still take care of them for a few days. When the fry are free swimming, then you remove the male.
You can have the sponge filter on now. You can feed the fry baby brine shrimp, then smal frozen food, then eventually graduating to flake food.
As they mature, you will eventually have to remove all the males into individual containers. This is where you can try to sell some, and keep who you want.