Uninterested describes someone who doesn't pay attention or care. If you're uninterested in touring old homes and shopping for antiques, you might be bored on vacation with your aunt and her friends.
The adjective uninterested is the one you'll use if you really don't care about something. You might be uninterested in the economics textbook chapter you keep trying to read, or uninterested in the celebrity gossip everyone is sharing. Uninterested is like bored. The Latin root word of interest is interresse, or to be of importance. So when something's not important to you, you're uninterested.