Galleries hold your actual photographs. When you upload photographs you always upload them into a new or existing gallery.
A gallery can have a description and access to it can be protected. Every gallery has a corresponding visitor page where visitors can view thumbnails and photographs.
Galleries can be organized into Groups. Groups are similar to folders on your computer: they can hold galleries and other groups.
You can create any number of groups and organize them into a hierarchy that suits your needs. Groups can be moved in and out of other groups at any time preserving the links and the content.
Collections hold links to uploaded photographs. They can include links to photos uploaded by you or by other Zenfolio members.
You can reference the same photo in several Collections without having to upload the photo many times. Collections are also great for saving together photos from several Zenfolio users taken at the same event or location. Or for collecting in one place your favorite photos on a specific subject.