A woman may become pregnant if a man’s sperm reaches one of her eggs.
Contraception tries to stop this from happening, it does this in various ways such as: by keeping the egg and sperm apart, by preventing an egg being released, or by making the womb not accept a fertilised egg.
You should always be honest with your doctor when getting advice on contraception, for example, if you smoke then this means some contraception will not be suitable for you.