How to get prep depends on where you live. A sexual health clinic like planned Parenthood is a good option. In terms of viruses that can be sexually transmitted there's HPV, HIV, HSV, and Hepatitis. Condoms prevent HIV but are not full protection for the other viruses. HPV does have a vaccine for the cancer causing strains but I think roughly 80% of sexually active adults have had HPV. The statistic is higher for HSV.