the sex

Question
how can you tell the sex of the beta fish because i don't know
and how often should i feed it?
is bottled water ok for it to live in

Answer
Hello Amanda,
You can find a lot of books in pet stores about betta care, as well as great information online.
You should have a two gallon tank or larger, a thermometer and a tank heater (you can buy small one for 2 gallons and up at Petco and sometimes at Wal-Mart), you need betta pellets -don't feed him for meant for other fish, they have specific needs - and feed him 2-3 pellets per day.
You would be better off using tap water with tap water conditioner, it's cheaper, and it will usually be better for your fish in the long run. Tap water has a lot of minerals in it that your fish need. Just make sure you use tap water conditioner! It removes the toxic chlorines and chloramines from your tap water and makes it safe for your fish. This can also be bought at pet stores and a small bottle should last you a few months.
You most likely have a male. It is very easy to tell male from female on bettas - males are more colorful and have long, flowy fins. Females tend to be smaller (though not always the case), are much less colorful, and have smaller fins.