Condoms can't prevent sexually transmitted diseases (STDs) or pregnancy 100% of the time. The only method that fully prevents pregnancy and STDs is not having sex.
But if you have sex, condoms are still the best way to protect against STDs (also called sexually transmitted infections or STIs). To protect yourself, use them correctly each time you have sex. Keep in mind that condoms won’t prevent STDs that can spread from parts of the body they don't cover.
For better protection from pregnancy, use condoms with a second kind of birth control, like birth control pills.
If a condom breaks or slips off during sex, you and your partner should get tested for STDs. The testing can be quick and is often done with urine tests or blood tests. Many schools have wellness centers where you can get tested. You can also go to your doctor or a health clinic like Planned Parenthood, where you can learn more about birth control.
If you might be pregnant, talk with your doctor or pharmacist. They can tell you about emergency contraception (a way to prevent pregnancy after unprotected sex).