What’s wrong with the bike My boy uses a bike for work all was fine until yesterday when he went to use it the pedals and chain go around ok but the back wheel doesn’t move
Daniel is right - it sounds like the mechanism in the back that allows coasting, has failed.    This means the chain is driving the cogs forward, but there's no connection between the cogs and the hub of the rear wheel.

There are no good fixes short of replacing the rear freewheel or freehub, depending on what the bike has now.   A deep clean and relube can help, but it may not, and even if things improve they soon deteriorate again.

To test this, take the back wheel out of the bike, and rotate the cogs by hand.  Yours will probably turn both ways, when they should only turn anti-clockwise.  When you try to spin the cogs clockwise, they should not move at all.

The replacement you need will depend on what you have.  Either show us a photo of the cogs when the wheel is out of the bike, or just take it to a LBS and ask for a new freewheel.  Its not a big job to fit to your wheel, but does take one or two special tools.

This is fixable.