Birth control is anything that prevents you (someone with a vagina and uterus) from getting pregnant. This ranges from abstenence and pull out method, which are both without any aide, to pills, condoms, shots, patches, and more.
If you're sexually active, there are a few things to take into consideration. Like if you and your partner are exclusive or if you're worried about sexually transmitted diseases/infections. If you ARE concerned, which is completely reasonable, condoms and dental dams (which are both latex or other stretchy material based protections that form barriers) are your best bet. Other forms that do NOT have a physical barrier include pull out (not very effective, I would advise against), hormonal patches, pills, IUDs, injections, spermicides, diaphragms, and probably more that I haven't thought to list. I would also err from injections, as they can affect long-term fertility.
Spermicides kill sperm cells in the vagina and are best as supplimental protection. Patches are left on the skin for a week at a time to regulate hormones to prevent pregnancy. Pills are taken daily to regulate hormones to prevent pregnancy. IUDs are intrauterine devices that can be hormonal or copper. Either way it goes up through the cirvix and prevents pregnancy. Diaphragms are inserted into the vagina before sex and removed after, it's a physical barrier that prevents pregnancy but not STD/STIs.
If you're NOT sexually active, birth control can regulate hormones that cause bad period symptoms and intense flows, and hormones that cause bad acne and other symptoms of hormonal irregularity. Be advised, however, that irregular use of things like the pill can lead to ovarian cysts, which are very painful. Generally, that isn't even an issue.
Google more about it or ask a doctor for more in-depth information!