How are the wheels spokes laced in the bikes you buy at shops? Is there a machine that does the lacing or does it have to be manual work? And in the first case, what does it look like and how does it work?

Manufacturers will use machines to build the wheels, however on top end bikes the manufacturer will build the wheels by hand (a skilled wheel builder's work is considered better than that of a machine). Your LBS will unlikeley have a machine to build wheels and this will be done by hand.

So in summary. New bike - wheel was most likeley build by machine. Repairs - wheel was almsot certainley built by hand.

As @arne said. You can search youtube for "cycle wheel building machine"