Outdoors, indoors, concrete floor, wood floor, skate parks, sidewalks, derby tracks and rinks. We've got a wheel for that!
Wheels are classified according to hardness and size- diameter and width.
Hardness is rated with a number from 78a to 103a. Lower numbers are softer and higher numbers are harder. Larger wheels will roll faster with less effort, smaller wheels are more maneuverable.
Don't forget to get some bearings when you get wheels!