In its many forms, sex is one way to explore a relationship.
Sex is a natural act.
Every person on this planet originates from sexual union, but while it's natural, the empty act of sex isn't very satisfying. The emotions which go with sex make the act magical when it's with the right person. There is no rule that says when you should start having sex. Sex includes far more than intercourse. Holding hands says a lot about whether you are attracted to someone.