Hello. Just bought a used bike, tires are in rough shape figured that changing them will be easy but I guess I was wrong because I'm very confused with all the different sizes.

Current tire size: 26x2.125
Rim: 559-21

I don't fully understand if I could say fit something like this on it: Continental Tour Ride 26x1.75 (47-559) or Maxxis Detonator 26 x 1.25.
It has mountain bike tires on it, but since I won't do any "mountaining" I would prefer city type tires.

And if I buy inner tube it should be same size as tire? Continental MTB 26x1.75/2.5 40mm tube would be compatible with the Continental Tour Ride 26x1.75 (47-559) tire?