Getting into powerlifting is as easy as it sounds: find a meet, get a league card, send in the entry form, go to the competition.
If you can find some local powerlifters from the league you plan on entering and have them check your form out beforehand. It's not necessary, but will make things a lot easier for you at the competition.
Most National and International meets will have some sort of qualifying total required, but local meets rarely do. Contact the meet director and they can help you out with the details.