A turnaround is a short chord sequence that is used to connect the end of a tune back to the beginning. On its own it is just a short loopable chord sequence, that can be used to improvise over. It has one main key (Bb in this case), but the transition chords also provide an opportunity to experiment with other scales.

So in fact you can play basic single key phrases, no problem, but the more comfortable you get, the more you can insert more advanced phrases, using specific chord notes or even multiple scales.