If you are signed up to receive them, on the 1st and 15th of every month, you will get an email from Mass Golf providing you with your 'Handicap Index'. This is an 18 hole index and is not golf course specific
When you post your score, you post it into the Golf Handicap Information Network (GHIN). The GHIN system tracks your scoring history, computes handicaps and facilitates fair competition among golfers
When the Pairings group creates the pairings sheet for a particular week, usually the first step they take is to update your index from the GHIN system. As part of the process, the system that is used to create each week's pairings (Golf Genius) takes your updated GHIN index and calculates your handicap for whichever course you are playing that particular week; either Starboard Back 9 or Port Back 9. On the Pairings sheet that is sent out, you will see both your 18-hole index as well as your course specific 9-hole handicap
There are certain tournaments where your GHIN index (and thus your handicap) will be frozen for the duration of the tournament. You will be advised when this is the case