you must get male - female, male - male or female - female who love each other into the same car. now you must click one and interact with the other. Then choose woohoo or if cuddle is there do that then woohoo
You have to first make sure they love each other enough to get into bed together. Once you've done that, make them both relax on the bed. Then, with them both relaxing, you can get one sim to...