What does this data mean?
RNP=required navigation precision
ANP=available navigation precision
Required Navigation Performance (RNP) is the navigation accuracy the aircraft must be better than. It can change automatically or the crew can manually change the values (such as during a RNAV (RNP) or RNAV (AR) approach).
Actual Navigation Performance (ANP) displays how accurate the FMS thinks it is. If the ANP is less than the RNP, you’re good! If the ANP is larger than the RNP, then your FMS will tell you your navigation accuracy probably isn’t good enough to fly in the airspace you’re flying in or using the approach you’re using. The smaller your ANP, the more accurate your navigation solution is.
EDIT: If you want to mess around with your ANP values, turn off GPS updating and Radio NAVAID updating in your FMS. The ANP will start increasing as the IRSs drift and the aircraft’s navigation solution doesn’t get corrected with GPS or radio NAVAIDs. Or you can fly into a GPS Jamming/Spoofing environment… but MSFS doesn’t simulate that…