1. at most basic: turnarounds are to add interest (relieve monotony) of the typical two measures of tonic at the end of a tune or section, and to 'turn' back to the beginning (or next section).
2. start with, for two measures of Cmajor, play | Cmaj7 Am7 | Dm7 G7 |.
then | Em7 Am7 | Dm7 G7 |
then | C6 A7 | Dm7 G7 | (or use A7b9 in place of A7)
then | C69 A7 | D7 G7 |.
learn in all keys, all tempos.
see aebersold vol 3 and 16.
3. sometimes composers put them in, sometimes they are improvised.
4. after you have a command of the basic, do what our resident pro reg suggests....
