My back wheel isn't connected to the gears
The bike is made by Univega and probably has a freewheel. 

If the pedaling motion still works, I'd guess your freewheel is shot (the thing that the gears are on in the back). You have to remove it with a freewheel remover and put on a new one. This requires a freewheel remover tool and a large wrench or vise, so you might want to take it to a shop and let them check it over and swap the freewheel out.