There is a little confusion on how to use the words use to and used to. One reason for the confusion is that it is sometimes used as a verb, and sometimes used as an adjective. The other reason is because it seems like the tense changes. It's really quite simple when you look at it.
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 to climb trees. (Now he doesn't climb trees.)
Remember, we always use this word when talking about the past. So when do you use use to without the d at the end? When the base form of the verb is used. Look at these examples- She didn't use to swim before noon. (Now she does swim before noon.) Or Did your father use to ride a horse? In these cases the past tense is shown with the did and didn't.