My garage was originally a two car garage . An addittional one car garage was added to the right . The original has a pitched roof and the addition has a roof attached to the one side of the original, the additon has a different pitch and starts about four feet down from the peak of original roof. I can not stop it from leaking where the two differen pitches meet. What can I do to stop the leaking

You probably might need to put flashing along there.

When the addition was built the new shingles should have been slid under the exiting shingles on the steeper pitch old roof. It sounds as though this was not done or at least not done well. At this point Nohelps suggestion is about all you can do unless you are ready to reroof.