Before you go out and pick up a betta fish, you need to gather some stuff for the tank, to keep your betta happy. You will need to keep in mind that female bettas can live together just fine, but they are not as pretty. Although male bettas are so pretty, they cannot live together at all. After you have decided which way to go, head out the the store and pick up some items.
Tank
Bettas can live in small fishbowls (you see the little cup they come in?) but will be way more comfy and happy in a bigger fishtank. When picking one out, make sure it is exactly what you want. A ½ gallon or bigger will work well if you only have one betta living in it.
Dividers
If you plan to have males and females together or more than one male, also invest in some dividers for your tank, it will prevent your fish from fighting, although they can see each other.
Gravel
You will need gravel for any tank you pick, it can be any color or size, it makes the tank look great and gives the plants and ornaments a place too sit. It also gathers all the dust and debris that falls from the fish. This makes cleaning much easier and many fish love to have the gravel to burrow in.
Plants
You do not absolutely need to have plants, but it makes the tank look well put together and much calmer for your betta. You can get real or fake ones, which ever works better for you. Real ones take a little more work though.
Gravel Vacuum/net
You will need the vacuum and net for cleaning (which needs to be done regularly) The vacuum can get all the little bits of uneaten food and such from within the gravel, without sucking the gravel up and out. The net is useful for if you need to pick up the fish or something.
Thermometer/heater
These are not absolutely necessary with bettas, but if you want to make them comfortable, it might be worth it. Betta’s are much happier with the water a little warmer, and the thermometer (maybe one of the ones that stick to the outside of the aquarium) will help keep it from getting to hot or cold.
Betta food
Although Bettas will eat just about any flaked food you put in there, there is special food just for them at any Wal-Mart or pet store. It makes them brighter and much happier. They also like freeze dried shrimp for a treat.
There is so many things you could buy, but it begins to add up and make it really expensive for you. Make sure to feed them daily, and clean their cage once a week or so.
References:
Aquariumguys
http://www.aquariumguys.com/betta-fish-care-article.html