I'm not sure whether this is a typo and you mean sex BEFORE marriage, but let me answer nonetheless.
1. If you mean sex BEFORE marriage, and you're wondering what can you do with your boyfriend or girlfriend physically, then I would say (and this may be hard for some of you to hear), to follow what 1 Timothy 5:1-2 says:
"Do not rebuke an older man harshly, but exhort him as if he were your father. Treat younger men as brothers, older women as mothers, and younger women as sisters, with absolute purity."
Additionally, ask the question, "Would Jesus be glorified or shamed if we did ______?" Young people, make sure you guard your heart (Proverbs 4:20) and guard your body for you cannot undue what has been done to them!
2. If you mean sex AFTER marriage, then you are mistaken. The Bible teaches that we are to enjoy sex (abundantly, freely) after we have committed exclusively and permanently to our husband or wife (aka marriage)! In fact, the entire book of Song of Solomon talks about sex very erotically and openly! Listen to an example of what is preaching from this text, by Pastor Mark Driscoll...
[Answered by Pastor HM, who is happily married]