Gallery albums contain all the images. Think of these just like a scrapbook type of photo album. Different albums have images from different things together to keep them better organized. While you wouldn´t usually have an album with just one of tow images either.

Albums will usually be created for an event, trip, meeting, or activity if there are going to be 20 or more photos. You may also want to consider adding more then one album if there are going to be a lot of photos (200 or more) The exact use and structure is up to the person structuring the gallery so these are just guidelines.