Birth control prevents pregnancy in a variety of ways, depending on which type you choose.
Some types of birth control rely on hormones. For example, Nexplanon is a thin contraceptive implant that releases a steady, low dose of hormones to prevent pregnancy. The pill also relies on hormones to stop your ovaries from releasing eggs.
Meanwhile, condoms, diaphragms, and cervical caps create a physical barrier to block sperm from fertilizing an egg. For added protection, some also use spermicides to kill sperm.