The shifts are easily swapable, when there is someone to swap with, which as far as I know is quite a lot of the time. There are always people who don't like earlies, some who don't like lates, the list goes on.
Job would start off as whats called an 'A3' this is the most junior customer service level. So you will be on the check in desks, meeting arrivals and also carry out gate duties.