I'm sorry to say, you can add a betta and that's about it. Are you cycling your tank or do you just have it running? Cycling requires adding 4ppm of pure ammonia and allowing the bacteria to populate in your filter to break that ammonia down into nitrites. From there, another type of bacteria will break down nitrites into nitrates. Once you can add 4ppm of ammonia and it be converted into nitrates in 24 hours, you can add your fish. You could also go and get a small bottle of Tetra SafeStart and your betta and add both at the same time (the entire bottle). It will introduce some of the bacteria.
Do you have a liquid test kit so you can monitor your levels? This is an important tool to have when keeping fish.
Do you have a liquid test kit so you can monitor your levels? This is an important tool to have when keeping fish.