This means the kind of 'legs' you must have in order to stand upright out at sea, on a constantly moving ship. In other words, to "get your bearings" or get used to how things work in a new environment that is unfamiliar to you. The idea is that you have to learn to get 'in sync' with the rhythm of the waves, or you'll end up on your backside : )

Sea legs* When someone doesn't have them it means they are not use to being on the water in a boat. When someone has there sea legs it means they do not get sick or anything while on a boat :).

finding your sea legs = learning to walk straight on a boat Now compare that to going into a new job, and you have it. How's Egypt, by the way?

Here it means to learn all about your job so that you can "stand on your own two feet".

gills ?