Make certain whomever is putting the outlet in understands that it's a 120V outlet for an RV, and not a 240V outlet for a dryer (or anything else). People, even people who should know better because they're paid and licensed to know better, sometimes get that messed up and it does not end pleasantly.
Generally, there's nothing you need to switch on in the motorhome once you've plugged it in unless you need to use something. The converter comes on when you plug in to charge the house battery and power 12V systems, while the 120V systems are powered directly from the shore power. On your motorhome, there's probably an automatic transfer switch that, when the generator is started, will disconnect the 120V power feed from the shore cord and connect it to the generator output. (If it doesn't have one, there will be a socket in the cord storage compartment to plug the shore power cord into, with the generator powering that socket.)
If there is no water in the water heater tank, be sure that the electric water heater switch is off before plugging in or starting the generator, or you will not have a functional water heater element anymore.