Ranks aboard the USS Iceni represent how hard an individual has worked and helped with the running of the chapter. If an individual is a member of SFI, it also represents their contributions to Region 20 and SFI as a whole. Promotions are done twice a year for all ranks unless stated otherwise, plus (so long as all other criteria are met) at the descretion on the CO, times held at each rank before promotion may be waived. You will notice two ranks listed for each level, one is the Starfleet ranks in order, next to that is the Marine equivalent.
NB – Although the CO will be keeping a note of all things done by members in order to gain promotion, ultimately it is up to you to make a note of everything.