This red movement block sets the object to face in a specific direction, no matter where it started from. This number always refers to the angle from the bottom of the screen. Use a shape like heart to see how it works. Setting the rotation to 90 degrees will place the heart on its side with the top edges facing to the right. Setting the rotation to 180 degrees will place the heart upside down with the top edges facing down.
For an example, search the community for Poring Dodge. This project uses this block to rotate the obstacles before the game starts.