What should you do when you see this road sign?

This blue circular sign with a white arrow pointing left is a mandatory direction sign in Germany. It means that you must turn left at the next intersection or junction. You are required to indicate left to signal your intention, and you must make the turn before or directly where the sign is located, not after passing it. Following these instructions ensures safe and legal navigation according to the German traffic regulations. In summary: indicate left and turn left as directed by the sign.