There's not a lot of explicit sex in this play, even between the two characters who are in love. When Miranda and Ferdinand meet secretly, they hold hands, and when Prospero sends them alone together to his dark cell, they play chess. Seriously.
Maybe this is because of Prospero's warning about what will happen to Ferdinand if he's all up in the marriage bed before the marrying's done, but in these kinds of conversations we catch a glimpse of how sex is discussed in the play. Prospero explicitly tells Ferdinand there's to be no fooling around before the marriage. Ferdinand, instead of being like "Dude, you're her DAD!" decides to tell Prospero that, when the wedding day comes, he's sure it will seem a super-long day, because he's so itchy to get into bed with Miranda.
Miranda has already suffered an attempted rape by Caliban, and Stefano hears about her in relation to the fact that she'll breed well. Besides Ferdinand's anticipation of his wedding night, sex is referenced as a good means to breed – this is the animal (or natural) way to view the act, instead of the courtly, romantic way.
The other sexual references in the play are mostly made in jest. Prospero teases that his wife was virtuous, and though he couldn't get a DNA test, he trusts that Miranda is the issue of his seed. A drunken Stefano sings a dirty sailor's song about Kate, who would let a tailor "scratch her where she itched." So that's a pretty good look at sex in the play – it's present, but under the skin of the text.