First- find a check list. There are lots of them around including on this site. You may modify the list after you use it awhile but I assure you, if you don’t use one you will eventually make a very expensive mistake.
Second, get the rig as level as possible. I have a long post about how to do that and I will send it to you if you like.
I agree with everything that has been said about the water. If I am hooking up to a campground post I put on a Y first. When I disconnect I turn off the water supply and open the unused side of the Y. Then I can disconnect the water from the trailer and roll it up. The water runs out the Y and then I disconnect and fasten the ends together.
I agree that you should not borrow your neighbor’s hose for any purpose and I would be very suspicious of any other advice he gives you.
Next electric. Turn off the breaker on the campground post, plug in your cord and then turn the breaker back on. If there is no breaker, I plug into the post first and then the trailer. Reverse the process when you pack up. Many of our members use a circuit tester before they plug in but I have never, in 30 years, felt the need.
When you leave, go to the dumping station, drain your black tank, hook up a green, black, brown anything but white hose to the tank flush, keep the drain open and flush until clear. You won’t know unless you use a clear adapter to hook hose to camper. Then drain the galley tank and finally the gray tank.
Enjoy and come back often