how do i take care of a beta male fish?

If possible a bigger tank. 1 gallon is really the bare minimum. if at all possible, get a bigger tank.
Flake food, pellets expand in there stomach and can hurt some bettas.
Cycle the tank- http://www.firsttankguide.net/cycle.php
Cover the tank, they jump!
Silk plants, never plastic. Plastic can hurt their fins.
After the tank is cycled. change 1/3 of the water once a week.
Nothing else in there with him. Tank is to small.
They like treats of frozen bloodworms, or brineshrimp one to two times a week.
If you can get a filter and a heater, or change 1/3 of the water twice a week after it is cycled and keep him in an area in your house that stays above 75F all year round.
Good luck!

Betta's are very easy to care for. You didn't say if the tank has a filter or not. You don't need one really just change the water about 1x a week you don't need a heater nor do you need an aerator. Just feed it everyday.

You need a heater because bettas will be healthy in temperatures in the high 70s (78-80)

Feed one pellet a day and skip a day so that he doesnt get digestion problems.

Provide a few decorations to keep him busy.

Change 25 % of the water each week.

That's pretty much it, al though i would recommend getting at least a 2.5 gallon tank.

Tank size: 5 gallons(no exceptions they are nto meant to kept in small tanks/bowls)
Essentials: Filter and Heater(they will die without one)
Water Changing: Once a week(twice a week is more desired)
Lighting: Only needed to enhance betta's colors
Eating Habits: All members from the betta family are very slow eaters
Plants/Decor: They love live plants such as Java moss, Java Fern, and at times bamboo. All decor most have soft edges or they will hurt his delicate fins
Food: Flake is fine but pellets are better due to the akward shape of it's mouth
Life Span: 5 years at the most
Tendancies: They tend to flare and fight with a mirror and they also bulid bubble nest used for mating but this doesn't mean he needs a girlfriend betta breeding is extremely hard due to all the violence

Well that's about it and I hope you have fun with your male betta!!!

Short answer, eh?

1. It should be in a 2.5 gallon tank or larger.
2. The tank should have a filter and heater.
3. Change 10-25% of the water each week with a gravel siphon.
4. Have some variety in their diet. They seem to love frozen bloodworms.
5. Try to find a cave or something he can hide in.

EDIT: If you do get bamboo, make sure that it's not fully submerged, and that part of it is sticking out of the water. It's not fully aquatic, and will die if its submerged.

pretty simple.
filter
clean water(scoop out and replace about a cup each day-tap water is fine)
food-those little pellets(azz it up with a thawed frozen pea with the shell removed)
the water should be kept warm.cold will kill them.
maybe fake plants to give him securtiy and to make it look nice
thats just about it.