There are 3 wheels to control things, 4 if you have an R lens with a control ring (or an EF adapter with control ring).
Here, shutter and aperture are "linked" to produce a proper exposure, so moving the front dial changes both.
Fv is a whole new thing that they call "flexible priority". It is pretty much the same as P mode until you decide to override the cameras initial choice. It offers a quicker way to "tweak" the P mode setting. You use the "thumb dial" (what I like to call the "mode dial" to select which thing you are going to override (shutter, aperture, E comp, or ISO), then you use the front dial to make the change. You can even fiddle with more than one of the "exposure variables", adjusting for example both shutter and aperture.
Important: to reset all the exposure controls to full auto, use the "trash can" button on the back of the camera. Press it to reset the currently selected thing to auto. Press and hold it to reset all the controls to auto.
The settings "stick" from exposure to exposure
The above video is quite good and he goes through much more than just the Fv mode. He goes through virtually every setting on the R5 and tells you how he sets up his camera. He is a wildlife shooter, so not all of his choices will apply, but he offers lots of good information.
The idea with Fv is that if you use P mode a lot (as I am doing more and more) and want to easily grab more control now and then, you can learn to use this mode and do so more efficiently. Alternatively, you can just ignore it.
Tom's Digital Photography Info / tom@mmto.org