Most people have sex some time in their lives. What should they know in order to protect themselves?
There are several ways in which people can protect themselves from sexually transmitted diseases/infections or unwanted pregnancies. If a couple wants to lower the risk of pregnancy, several barrier methods can be used to prevent the sperm from reaching the egg. Male and female condoms are options. IUDs are also extremely effective. The morning after pill will delay ovulation for a bit, but it won't work if ovulation has already occurred. Birth control pills are also very effective at preventing pregnancy.
Most birth control methods are effective at protecting the couple from pregnancy; however, they are not effective at protecting the couple from sexually transmitted diseases/infections. Condoms do this because they prevent the passing of fluids from one partner to the other and, when used correctly, they are the most effective way to prevent STDs/STIs.
One thing the couple should know is the past sexual experience of their partner. If one partner has had multiple high-risk partners, they are also a high-risk partner. That person should be tested for STDs/STIs. If that partner tests positive, the couple can make an informed decision about when and if they should have sex with each other.