One needs to become accustomed to something. For example, We've always had a small car, so driving a big van like this—well, it takes getting used to. This idiom employs used to in the sense of “accustomed to,” a usage dating from the first half of the 1500s.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.