AN INST PLT RIDING AS A PAX DID NOT UNDERSTAND SEVERAL ASPECTS OF INST FLT; WHICH CAUSED MANY ERRORS FOR THE PF; INCLUDING VFR IN IMC.

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PRIOR TO DEPARTING ON AN INST FLT PLAN; THE CEILINGS AT THE DEST WERE FORECASTED TO BE SIGNIFICANTLY ABOVE MINIMUMS; AND ATC SAID THAT NEARBY ARPTS WERE RPTING MARGINAL VFR. WE HAD BEEN DELAYED FOR A FEW HRS BY STORMS; SO THE TWR AT GPM WAS ALREADY CLOSED. AS WE MADE THE APCH; WE BROKE OUT JUST ABOVE MINIMUMS. WE CIRCLED THE FIELD TO LAND; EVEN THOUGH THE APCH WAS NOT APPLICABLE FOR THE CIRCLING MINIMUMS. THERE WAS SOME CONFUSION THAT AROSE; BECAUSE THE APCH ALSO HAD THE NOTATION 'FLY VISUAL 1.9 NM' ON THE FINAL APCH PATH. I THOUGHT THAT THIS MEANT THAT ONE COULD CIRCLE AS LONG AS ONE KEPT THE FIELD IN SIGHT; AS WAS DONE ON PREVIOUS TRAINING FLTS; ALBEIT IN VFR CONDITIONS. ALSO; AFTER LINING UP ON FINAL; WE SWITCHED FROM UNICOM TO APCH FREQ; AND CANCELLED THE IFR FLT PLAN PRIOR TO LNDG; WHICH WE LEARNED AFTERWARDS; CANNOT BE DONE UNLESS FLYING IN VFR CONDITIONS. I BELIEVE THE MAIN CONTRIBUTOR TO THESE EVENTS WAS THE ABSENCE OF FORMAL TRAINING REGARDING THESE ISSUES. FURTHER TRAINING REGARDING THESE AND OTHER DETAILS OF APCH PROCS SHOULD PREVENT THESE PROBS AND SIMILAR ONES FROM OCCURRING.