I always get confused with Unreal rotations for, say moving lights.
This diagram explains it to me.
Imagine standing on a glass floor, underneath your feet a spotlight hangs down.
-90 Pitch (Y) means the spotlight points straight down. Increasing pitch to 0 brings the spotlight up to point along the floor. Going to positive numbers points the light up, at 90 it’s pointing straight up.
Yaw (Z) makes the light rotate around to points of the compass.
In the pic I’m facing south- represented by yaw 180, the spotlight is pointing downwards at -20 Pitch with 90 Yaw so it points east