Ah, the Betta. Also known as the Siamese Fighting Fish, or it's Latin name Betta Splendens. A very beautiful fish. With it's highly visable colors, and flowing fins, it is one of the most recognizable aquarium fish. However, there are some rules when keeping one.
First and foremost, you can only keep one. Any more than one, and they will fight to the death. These things happen. Women are very jealous fish.
You can also keep one in a small bowl, but they do better in a bigger tank. But once you give them a bigger tank, they will want castles with air bubbles. In fact, it's suggested that they want a nice big castle. Also around that castle they also want lots of plants. Maybe some nice landscaping rocks.
Remember to clean the tank, and cut the grass er, algae. Keep the enviroment nice, and control the temperature between 75 to 83 degrees F. You will also have to spend the money on higher quality frozen or live foods, instead of flake food.
Keep an eye on your betta, give her plenty of natural light, and she will do well.