The NuvaRing, the Patch, and some types of oral contraceptives contain a combination of 2 hormones - estrogen and progestin. Some pills can contain only progestin, but these tend to be less effective.
Estrogen and progestin are hormones that are already found in the female body but when a woman uses hormonal birth control, her body sees that there is already enough hormone in the bloodstream, so it decides that it doesn't need to produce anymore.
These kinds of birth control give your body a stable dose of hormones each day, so the levels in the body don't change. It's the fluctuation of hormones that make ovulation happen. The reason hormonal birth control works so well is because the stable levels of hormones prevent you from ovulating. If your ovaries don't release any eggs, then sperm can't fertilize them and you can't get pregnant.
Dear's Advice: If you're using hormonal birth control and you don't want to get pregnant, be responsible and remember to use it properly and consistently. Missing pills, or forgetting to change the NuvaRing or the Patch can cause you to ovulate resulting in an unplanned pregnancy.