First time, they'll look at you like you've completely lost the plot. That's normal, and it's the bit most people get wrong, they push, the dog digs in, and the cup ends up in a cupboard.
So don't rush it. Keep a few treats by the door and let them do the work for you.
Day one - leave it out and let them sniff it. Treat. That's the whole of day one.
Day two - one paw in, no water, straight back out. Treat. Thirty seconds.
Day three - warm water, one paw at a time, treat after each. Never cold water; that's where it usually goes wrong.
Four paws, four treats. Dogs work out that arrangement remarkably fast.
By about day three, something quietly brilliant happens. They stand on the mat and give you the paw before you've asked - and after that you can drop the treats entirely, because the routine has become the routine.