[kozzy]

Welcome.
yeah better off asking questions here. When I had an issue with my backup camera, that was proof about the "things being different from rig to rig" I don't think they have consistency on the way they do each rig. Your RV is not to much different on the plumbing/electrical side from your home, as far as the basics. Get a good multimeter to help troubleshoot electrical issues. 12v is easy, positive and negative. 120 AC is a little more involved, but if you have basic knowledge of electricity and how it works in your house, you can have good success troubleshooting some issues. and some basic plumbing tools to fix minor issues.
As for your issue, fill the water tank, and run with the pump on. if that makes a big improvement, its a safe bet that your fixtures and most plumbing is OK, and that the problem lies in a check valve, pressure regulator, or just not enough incoming pressure from your source.

One last thing, there are several RV maintenance and repair guides out there, I have 2 myself that I carry with me, that can help you troubleshoot and repair many things in your camper. I have one published by Bob Livingston (the industry expert) that is very detailed. Of course its in my camper, and I am at work at the moment, and cant remember the name. Good manuals to have though.