So how does a Spring Washer actually works?

Spring washers use tension force to lock the nut into place. As the washer is tightened under load, the vertical cut ends of the washer grab the nut and bind against it.

When the nut is fully tightened, the split in the washer should still be slightly out of alignment.

This is visual proof that the spring washer is still operating as intended and actually exerting a force on the fastener.