Next time please start a new topic rather than posting to an old - especially since your question is not related to the geoditic system in the title.
To save the latitude and longitude you need to create variables in the data dictionary for them and then assign the results of the GPS reading to those variables. Make sure the variables are long enough to accommodate the full range of latitude and longitude. I usually use length 13 for latitude and length 14 for longitude with 9 decimal places for both.
Assuming your dictionary variables are named LATITUDE and LONGITUDE the code to save would be something like this:
if gps(read, 60) then // Read for up to 60 seconds
LATITUDE = gps(latitude);
LONGITUDE = gps(longitude);
errmsg("GPS signal could not be acquired");
Note that you do not have to put the variables on a form unless you wan't the user to be able to see the numeric values but if you are just showing them on the map you may not need to.