You got to go jail first. Common beginner mistake: jail and prison are not the same, so don't commit a felony. Do something small like public intox or misdemeanor shoplifting or vandalism.
Jails have a special area for booty banditry called "the showers". As a noob in the jail, try and find a younger and weaker inmate to plunder. Or find an older weaker one. Either way, don't start off with big black Tyrone. That's hard mode.
Once you've asserted your dominance over three or four easy targets you will start to get a reputation. This is known as a 'rep'. Give yourself a cool nickname like 'assmaster' or 'anal annihilator'. Your concubines should start paying you in honey buns and coffee by now. You can use these goods as trade to the bigger blacker inmates for an opportunity at ravaging their balloon knots.
Basically it's like chess.