The only 100 percent sure method is total abstinence (NO SEXUAL INTERCOURSE): no sexual intercourse means no worries of pregnancy or STDs. The other methods of birth control, in order to be effective, must be used correctly each and every time. No matter which method you use, males should ALWAYS use a latex condom to prevent STDs.
Here is a description of each method that will be helpful to you when you see your own health care provider:
Norplant uses several small plastic capsules that are placed just beneath a female's skin in her arm. It lasts for five years and contains a contraceptive hormone that is constantly released so you don't have to worry about taking a pill everyday or getting a shot every few months. It takes about 30 minutes in your doctor's office to insert the capsule. Norplant causes you to to lose your regular monthly cycles and is over 99% effective in preventing pregnancy.
Depo Provera is a shot given to a female that contains contraceptive hormones and lasts for three months. It also causes you to lose your regular menstrual cycles, to be replaced with irregular menstrual bleeding or none at all. In my experience it does not cause hair loss or headaches (common rumors). Depo is around 99 percent effective in preventing pregnancy.
Oral Contraceptives (Birth Control Pills) contain hormones and must be taken by a female every day. If you forget many pills they will not be effective. You continue to have monthly periods on the pill and they are often lighter with less cramping. If you take pills properly they are about 98% effective in preventing pregnancy.
Nuva Ring is a soft, flexible ring about two inches in diameter. It's inserted into your vagina once a month and kept in place by your vagina muscles for three weeks. It releases a low dose of the hormones needed to prevent pregnancy and is 99 percent effective.
Otho EVRA is a very thin, beige, smooth patch that measures 1 3/4" on each of it's four sides. It releases a low dose of the hormones needed to prevent pregnancy and is 99 percent effective.
Condom and spermicide
A condom is a latex barrier that fits over the penis. Spermicide is a chemical usually in the form of a cream, jelly, or suppository (soft bullet like thing that melts when you put it in your vagina). Spermicides kill sperm and must be placed in your vagina before you have sex. The benefits are that the female doesn't have to take hormones to keep from getting pregnant and a latex condom will protect against STDs. Condoms and spermicides are available at most places like Target, K-Mart, drug stores and even some gas stations. You do not need to be any special age to buy these products, and condoms only come in one size (they all fit). Going to a cashier more your age might make it easier (less embarrassing) to buy these products.