It's called "Woohoo." And yes, you can. It an be done between two Sims of the opposite (or same) gender that is above the Teenager life stage. The preferred place is a bed but it can also be performed in hot tub, changing booth, car (Nightlife), photobooth (Nightlife), elevator (Open for Buisness), tent (Bon Voyage), sauna (Bon Voyage), hammock (Bon Voyage), helicopter (Apartment Life), and a closet (Apartment Life).