This is what you're playing the game for, isn't it?
fuck <person> will allow you start doing the nasty with them, if they've allowed it. Fuck is modified by your endurance and senses. To fuck something, you must have the horny status. If you happen to be female, and your partner is male, he will need an erection (have the horny status) in order for you to proceed. Every time you initiate and finish the act, you have a chance of gaining an IP in fuck. Once you reach orgasm, you will gain the endorphins status effect. This is the refractory period (TATOE) and you must wait for it to pass before before getting horny again. Endorphins will restore your health: fucking is the new "QUAFF POTION". Remember to remove <clothes> or remove all, and help your partner out by strip <item of clothing> from <person>. Heterosexual intercourse (yuck!) can result in pregnancy but luckily, there is a known cure.