You can definitely do it yourself if you feel comfortable. If not, your vet or a groomer can do it for you. There is usually a small fee, but nothing too outrageous.
Basically, hold the kitty and gently push on each paw to get the nails to come out. Take a look at the nail - most of it will be clear, except for a pink part. That pink section is called the "quick" and contains all of the blood vessels that feed the nail. If you cut into the "quick", it will cause pain and bleeding. It's best to cut off just the sharp end of the nail, but as long as you do not cut into the quick, you can cut back farther. Don't forget - there are 5 nails on the front paws. The 5th nail is located off to the side of the main nails - almost like our thumb.
You can use human clippers since a cat's nails are about the same thickness of ours, but it's best to use clippers designed for cats. The blade is shaped differently and helps prevent splitting of the nail when cut.
If she goes outside at all, you probably won't have to trim them as often. If she's strictly indoors, I would recommend doing it every few weeks, and also getting her something to scratch on, like a post or cardboard.