How do people get dressed so quick for plays and drama productions?

I know when people are in plays they get dressed super quick for a different scen and i want to know HOW!!!

Either double dressing (having one costume over another) or a quick change. Also, there are dressers backstage who have the costumes ready. The fastenings on most costumes are snaps and zippers. A lot of times dresses are in two sections: a bodice and a skirt.