First of all, keep the camera as dry as you can, even if the weather gets wet. Normally, some good heavy pieces of clear plastic over the top of it will do most of that. Then, after you finish shooting, you store your camera into the dry bag. Before you seal it, you toss in one or two desiccant packs (typically made out of silica gel), then seal it tight. The packs will absorb any stray moisture out of the camera or out of the bag. Then, you use the camera again and repeat the process with fresh packs. Now, after a while, you are going to have a bunch of used packs that are each holding some moisture. When you get home, you put the used ones on an aluminum pie tin and place it in an oven at 250 F. Leave it for an hour, and they are recharged (dry) and ready to go again. But, if you leave them laying around, they will absorb moisture again. So, upon removal from the oven, you put them in an air-tight bag and seal it for storage until you need them again. This is done a lot if you are taking your camera to a humid tropical jungle.