when starting car it sounds like a belt slipping. what would that be.

HAVE BELTS CHECKED FOR TENSION AND PULLEYS CHECKED

It could be the belt slipping. Open the hood and inspect the belt. Should be clean, flat black (not shiny) with no cracks. Check the belt tensioner by finding a section of belt you can pull on. Is it easy or difficult to pull. Easy pull means you should replace the tensioner as well. That'll be $50 bucks.