As a teenager, anal sex was that thing you either swore you would never do because it was gross or the thing you thought you had to do because it was cool. But in reality, anal is just like any other sexual activity — some people like it, some people hate it, and some people have absolutely no idea how to do it. This guide will cover all of the basics and answer your most important questions about butt sex. Anal sex is any sexual activity that involves the stimulation and penetration of the anus.