i would suggest you head over to the betta section of the forum.
However I do have some knowledge on this...
First you can end up with over 100+ eggs are you ready to take care of those babies? You will need a spawning tank (10 gal) filled half full with a heater set to just under 80 degrees, (your male and female betta should be kept in minimum 2 gal aquariums with heaters, incase they are already not kept in them), sponge filter, plants. Also betta babies only accept newly hatched brine shrimp. So you will need to create your hatcheries and have two or three of them setup so your babies dont starve. Also you will need to condition your bettas and get them ready for spawning, letting the female see the male, give them both live or frozen high quality food.
Then most people introduce the bettas into the breeding tank at the same time, however to protect the female many place the female in a chimeny or jar so she doesnt get hurt while the male builds his nest. So the male and female are seeing eachother, the female is getting full of eggs, the male is blowing a BIG bubble nest. It will be time to release the female. You will release her and she make chase and nip the male, the male may nip and chase her. They will both probably have damnage to their fins or could even die, so you will need to make sure you have individual aquariums for them, with a heater, bettafix or melafix, lots of fresh water and aquarium salt. After their forever long courtship the male and female will embrace over and over squeezing the eggs out of her, he fertilizes them then grabs the eggs and blows them into the bubble nest before they hit the tank bottom. (It should be barebottom by the way). When their courtship is over you will want to gently remove the female and place her in her tank, with a heater, medication and salt. You will want to have a light over the aquarium the whole time so the male can always see the eggs. You do not feed the male during this time. After a few days the fry will become free swiming and you can remove the male. Then you will need to feed your babies live food, microworms, baby brine shrimp, anything living basically. You will want to turn on the sponge filter at this time. You will need to make sure not to overfeed them because your babies can get swim bladder disorder, slowly fill the tank with water to the top. You will also need to syphon the bottom of the tank daily to remove any uneaten food.
Also just a note, you could possibly end up with lots of bettas, and viel tail bettas (the most common petstore type) don't bring in a lot of money, many petstores may not even take them. So you could be left with a lot of extra bettas. Also your female or male could die. Just a lot of preparation and things to consider before you beign to breed. I am no expert some people may disagree with somethings mentioned. But feel free to add anything i may have missed.