Lights , vent fans, water pump, heater thermostat controls, heater blower, fridge controls... Are 12v
Your duplex outlets are 120v and work if your are plugged into shore power or if your generator is running
Look at your shore cord
If it has (3) blades/prongs, it is 30 amp RV service
If it has (4) blades it is 50 amp service
You plug into the one it fits
30 amp , Max total power 3600 Watts
That's means you do not run a/c , hair dryer, coffee pot at the same time
Use only one large big draw item at a time
Make coffee, then use the MW or toaster
Turn off the a/c when you need the mw or hair dryer
Out side of that is just a matter of power management
If you have 50 amp RV , and are plugged into a 50 amp service, you can usually use any combination of of appliances and not worry about it