Visibility is what the bloke in the tower can see out of the window.
RVR is the runway visual range, usually measured by a fancy lasor somewhere near the runway.
RVR is relevant to all instrument approaches, whether a precision approach (PA) or Non-Precision approach (NPA). For planning purposes (i.e. destination alternate) the ceiling must be taken into account for Non-Precision approaches.
You take the higher of the obstacle clearance altitude, and the system minima, and use that to determine the minimum RVR required to fly the approach based on the airfield lighting available.
A typical minimum required RVR is 550m for a CAT 1 ILS with a decision height of 200', and 1200m RVR for a typical Non-Precision approach, for example a VOR/DME approach, with a minimum descent height of 400'.
If you do not have the required minimum RVR reported by ATC, an approach ban is in force. You may commence an approach, but not go lower than 1000' above the airfield level without the minimum RVR being reported.
This used to be the final approach fix or equivalent position for those without a fix, but it changed to a blanket 1000' above airfield level.
For single pilot operations, the minimum RVR for any approach is 800m, that's probably where you got that figure from.
At the other end of the scale, CAT 3B ILS with two crew requires the aircraft systems, airfield systems, and crew to have the capability/qualification/recency to meet the requirements, but has a minimum RVR of 75m.
If RVR is not available then reported visibility can be factored, 1.5 x vis for daylight, 2.0 x vis for night. A visibility lower than 800m cannot be factored.
https://www.easa.europa.eu/system/fi...May%202017.pdf page 64