STDs are diseases that can be transmitted sexually through intercourse, oral or anal sex, or childbirth. They may not show symptoms right away. Common STDs include gonorrhea, herpes, HIV, and chlamydia. The best ways to prevent STDs are to use condoms consistently, get tested regularly, avoid risky behaviors like sharing needles or having unprotected sex, and get to know sexual partners and their histories. Sex education is important for prevention but many schools focus only on abstinence.