Here is what you do
1. Draw something, like 2 squares then command + G (to group the drawings)
2. Click on the frame you want the animation to finish and click F5 (Insert Frame, in this case lets imagine its frame 10)
3. Next right-click on the grey area between frame 1 and frame 10, and select Create Motion Tween.
4. Click on frame 10 and select Insert KeyFrame (or just click F6 to insert Keyframe)
5. Now, for the rotation, you just click on the last frame (Frame 10) and rotate the square as you wish.
6. click Enter and there you have your rotating animation! 🙂