So, congratulations! You've bought all your supplies and you're ready to set up your tank. Here is what you need to do next.
It's a good idea to rinse everything, especially if it's been sitting for a while or was just bought from a store. This includes the rocks, the plants, the tank itself, and the pump (you only need to rinse the part that goes in the water). Do not use bleach, as it is bad for fish. If you need to sterilize it, put it in the hot sun for a natural bleach.
Be careful of the water
You don't need special water, but you do need to make sure the water you're using is clean. Sometimes, I trusted the tap water, but other places I didn't. Sometimes I found it easier just to buy the gallon containers of "spring water" from the store - especially if the sink I was using was too short to stick my tank under. It's okay to use tap water but you have to treat it before you put the fish in (the same goes for spring water). I used a brand called AquaSafe, which is in a bright yellow bottle. You can find it and other comparable products at a pet store. You don't need a lot - follow the directions on the bottle, and fishy should be happy.
Ich (also spelled ick) is a parasite that is common in aquarium fish. It looks like white, cloudy splotches on your fish, and will kill your betta if not treated. (microdermabrasion won't help this fishy!) The best way to prevent it is to put non-iodized salt (found at grocery stores) in your aquarium whenever you do a water change. I haven't been able to find a specific amount, but I think about a teaspoon for a two gallon tank is good. The salt will kill the ich without hurting the betta. If your fish does get ich, you can buy medicine at pet stores. I know Zeke (the first one) got tail rot one time and I bought these drops at Petsmart that made him all better and he lived for 2 more years. (I had him for a really long time!) The drops weren't too expensive either.
Put it all together
Once you've set up your aquarium, added your rocks, plants, water, water conditioner, and salt, you're almost done! Turn on the filter (or air stone, which is what I had) and let it run for a bit - particularly if it's the first time you've used it. It might be helpful to buy an aquarium thermometer to help you monitor the temperature - you'll want to make sure it stays between 75F to 82F (bettas are tropical fish). Don't put a heater in a tank less than 5 gallons, so be sure to keep your tank in a place that is warm enough for the water to maintain that temperature. (I never had any problems with this).
I let my aquarium run for about 24 hours when I first got Zeke. I wanted to make sure the salt and water conditioner got a chance to filter all through the water, and that the water was properly aerated and at the right temperature. The first time I added Zeke to my tank, I did it cautiously as the internet sites told me - adding a little bit of the water from the tank to his temporary bowl, a bit at a time, until all the old water was gone. Every time after that I just plopped him in. :-)
For subsequent water changes, I always let the aquarium run for a few hours before putting Zeke back in.
This is all I'm going to write for now on the subject, but I'm sure I'll revisit betta fish in the future. :-) Enjoy your new fishy!