Different methods, different points of action
Contraceptive methods prevent pregnancy by interrupting the process at different stages. Combined hormonal methods, which contain both an estrogen and a progestin, work mainly by suppressing the hormonal signals that trigger ovulation, so no egg is released. Progestin-only methods rely more on thickening cervical mucus to impede sperm and on thinning the endometrium, and they may also suppress ovulation depending on the dose and type.
Intrauterine devices act locally within the uterus, copper devices by creating an environment hostile to sperm and hormonal devices largely through their progestin effect on mucus and lining.
Barrier methods and choosing between options
Barrier methods such as condoms physically block sperm from reaching the egg and are the only common methods that also reduce transmission of sexually transmitted infections. Methods differ substantially in typical-use effectiveness, side effects, and suitability for an individual's health history.
This is general educational information about how contraceptive methods work, not medical advice; the right method depends on personal medical factors and should be chosen with a qualified clinician.