A turnaround is basically a chord sequence that gets you back to the main chord sequence of a song. They can be created with any chord sequence, but commonly the turnaround ends with the V or IV chord of the key the main chord progression is in. So if the main chord progression is in the key of A, the turnaround will end with either an E7 or Dmaj or Dmin chord.

Translating a chord sequence to another key. Say you have a sequence like A D E7 in A major, and you want to play the same sequence but in the key of E major. My way is to look at what each chord is relative to the key center (key). So in A major (key center) A is I, D is IV, and E is V. Then I think of what I-IV-V is in E major. Which is E, A, B7. make sense? It's alot easier if you look at it on the guitar because moving through keys is basically just playing the same pattern but up or down on the neck.