Woman
If a woman had sex with a man, and no contraception was used, there's the risk of her getting pregnant. If she does not want to get pegnant,  she has some time to take what is called emergency contraception. Emergency contraception protects against unwanted pregnancies, as it keeps the pregnancy from starting. It does not protect against sexually-transmitted diseases. Also, it will not work all the time. Very often, women who want to get emergency contaception also need to spend some time with a professional in a counselling session. Depending on the country, emergency contraception may not be available, or it may not be legal.