Some RV's have an automatic transfer switch that switches the coach from shore power to generator when the generator starts up. If your RV does not have an automatic transfer switch, you have to plug your shore line into the outlet to get power from the generator to the coach.
Codes require either an automatic transfer switch or physical disconnection and forbid wiring the generator directly to the coach so you can't inadvertently run the generator while the shore line is plugged in, backfeeding the pedestal. This could shock someone who is working on the system with the power supply off. At the least, the AC current from generator would not be synchronized with the power grid. That could make a mess!