You should really do as much research as possible before you even consider breeding. It's a very expensive undertaking in terms of time, money, and space in your home. Part of this is not only researching techniques for spawning and raising fry successfully, but an understanding of how betta genetics work so that you actually get what you want from your pair.
I don't recommend using pet store fish because 1. You don't know their history--so the results are unpredictable, and the quality potentially poor 2. They've likely faced poor conditions at the pet store and the fish farm and may not be up to it health wise 3. Age. Most consider fish over a year old to be past their breeding prime. Many fish in the pet store are already adults because adults have more eye-catching fins--so if you've had your fish awhile, he may be too old for breeding 4. Whenever we go to the pet store we see tons of beautiful fish languishing on the shelves because no one wants them--since you use fish from the pet store, your fry will be no different, and since you don't have the front of a big retail store, you'll probably have a very hard time finding homes for them, and you definitely shouldn't expect to make money off them.
If you're still interested, you should do more research into genetics. Here are a couple of good starting points: