What do you do upon seeing this traffic sign?

This traffic sign means "Yield" (Vorfahrt gewähren). When you see this sign, you must slow down and be prepared to stop if necessary. You must give right of way to cross-traffic on the priority road, regardless of whether you are turning or going straight. Your selected answers are correct: you need to approach at a moderate speed ready to brake, and you must let cross-wise traffic go first. Even if you are turning right, you still have to yield. This rule ensures that traffic on the priority road always has the right of way.