2003 Laguna DCi...Power steering belt controls what?

Hi, my mate is trying to sell me his Laguna DCi Estate.

He said that the power steering has stopped working and that when he looked under the bonnet, the belt had snapped.

Is this belt connected to other stuff?
Is it likely to have damaged anything?
Can it be driven as it is?


Thanks

2003 Laguna DCi...Power steering belt controls what?