The job of a spotter is to prevent the climber from landing on their head and (if possible) ensure they land on their feet and on the crashpad. This may involve moving the crashpad (which should coincide with the climber having a secure hold or position.
The job of a spotter is not to "catch" the climber! That's something they're simply not going to be able to do and attempting so can only lead to injury.
Consequently, the spotter should not be standing directly below the climber. They should stand so that they can push/guide the climber towards the crashpad and keep them upright / keep their head away from the ground.
This is usually best achieved by keeping their arms mostly extended, the heel of the hands towards the climber, fingers slightly bent backwards and the thumbs lying against the palm, not extended.