wmbuRn created a Timeline with a Float track that runs from 0 to 360 over 10 seconds. When Timeline plays, it increases value from that Float track each tick. output (in this case Windmill Spin) is linked to Z value of a Make Rot node (Make Rotation), essentially creating a new Rotation value. This value is then passed to Set Actor Rotation, which references Windmill. So every tick of Timeline, a new Rotation is given to Windmill blades, presumably.
As long as pivot point is in correct position on mesh you want to rotate, this basic idea should work for you. It sounds like you want something that will swing back and forth consistently, like Poe’s Pendulum, so you’ll need to make some adjustments.