What is the difference between indoor skates and outdoor skates?
For real, end of story.
Oh, you want more? OK.
Indoor wheels are harder, how much harder depends on your preference, but most wheels are 90A – 103A hardness, which tells you how much grip there is to the wheels.
An outdoor wheel is going to be in the 70A-85A range typically. This allows you to skate more smoothly when skating outdoors, since there are usually more debris out there, small cracks/pebbles and the like.
Do I need to have anything else that is just for outdoor skating? I always recommend having a set of bearings in your outdoor wheels just for that, but otherwise everything can stay the same! I usually will wipe mine off after an outdoor skating adventure. You also may see that your toe stops get used up faster when outdoor skating due to the rough texture of concrete.
So what are you waiting for? Get out there and skate!