hello
yesterday i was flying the 737 (ifr) with the autopilot and i was "playing" with the gps. I found an option which allowed me to fly direct to the airport (the fly was from bilbao to bristol and i was over the sea in that moment) and i activated it.ok it told me the new heading i switched the nav-gps buttom to gps and i turned on the nav buttom and it flew this heading but then i found an option which allowed me to select an approach i selected runway 27 and i could see 9in the gps`s flight plan the headings, distances... i activated it and put the switches on (gps and nav in the autopilot) but it did not approached correctly.Can anyone explain me why? how can i use in a correct way these options? can anyone explain me the use of the gps with all its options? Thanks and excuse me for my english

Well, as with real GPS units, you have to make sure you activate the appropriate execution for the approach.  Some may call for full procedure, DME arc, different waypints etc.  so when loading the GPS, it will ask how you want to initiate the approach.  One of the options they always give is vectors, to which it will simply give you directions directly from either your last waypoint in the flight plan (if you simply load the approach, rather than activating it) or a direct route from your current location to the initial approach fix for the approach. 

Also as mentioned you need to have NAV 1 set up for the ILS/LOC if you're doing that type of approach, as the GPS is not a substitute for those. 

Lemme know if what I just said makes sense and answers your question.   I wasn't exactally sure what answer you were trying to get.

It took long enough..