How to double tongue on the trumpet?

My lesson teacher told me to work on learning how to double tongue over the summer, and I'm so confused. I'm not sure at all what to do! I really want to learn how to double tongue because I'm now going into high school and I would love to be able to play more challenging solos, I'm really hoping to be able to play a Class A solo this year, and I would also love to be 2nd chair again. Any suggestions/tips would be greatly appreciated!!!!