If you can safely operate a handgun in 9mm or larger you can play. You will need a holster for said handgun, mags (the more the better) ammo (probably a minimum of 100 or so, but more is better here as well, 200 will do) mag pouches, and eyes + ears.
Classifiers are short standardized stages used to rank the skills and abilities of USPSA member, sort of like a handicap system. You will not need to be a USPSA member to shoot a local match.