How do we get Required RVR or Actual RVR for an instrument approach? When executing an instrument approach, when the pilot should start reference the RVR reported. Also, How do we get the required RVR for the current approach in execution and actual RVR. I think actual RVR can be part of METAR data. But I am not sure on the required RVR.
Current RVR is obtained from the METAR, yes, which in turn is obtained from transmissometer(s) on the airport site.

Minimum allowable RVR is obtained from charts (chart legend from Jeppesen, PDF), more specifically the instrument approach plate for approaching an airport. And on the SID chart for departing.

Example:



R is RVR in hundreds of feet, V is Visibility in miles, in this example. Units can change and will be denoted, check full PDF for all examples.