Used as an adjective. Use to be + used to. This means to be accustomed to. For example- I can study with the TV on. I am used to it. It means I am accustomed, adjusted, or don't mind having the TV play while I'm studying.

Or another example- Tim had a hard time living in Tokyo. He wasn't used to so many people.Tim didn't have experience being with big crowds of people before.

Used as a verb. Use to + verb is a regular verb and means something that happened but doesn't happen any more. It uses -ed to show past tense. But since it always means something that happened in the past, it should always use past tense. For example- I used to go to school in Paris. (I went to school there before, but now I don't.) Or, When Joshua was a child, he used toclimb trees. (Now he doesn't climb trees.)

The Canadian College of English Language