Yep, cycling allows for bacteria to colonize which helps regulate your tank overall. It benefits everything from fish to plants and it allows you to not have to do large water changes all the time. So it's always a win with cycling. :)
Although LoneHowler is right, I don't necessarily recommend getting anything from your fish store unless you know they take extremely good care of their tanks and don't have any sick fish. That would be a great way to bring home diseases and what not so be warned!
This link provides both the way to do it fishless or with your betta in it. Personally, I have cycled with a betta in the tank and they've done just fine. You'll need a test kit, or if you don't want to pay for one, you could bring the water to the petstore and they will test it for you. But whenever you test and you're cycling with fish, if you see any ammonia do a water change. That way it doesn't harm them. It might make your cycle time a little longer, but it's worth it to keep your fish alive.
After your tank is cycled (4-8 weeks) you could just do one weekly water change a week using a gravel vacuum. You'll want to at least change 20% of the water a week.