The source list is the area in blue on the left of the main Pomoto window. This list presents your iPhoto albums as a tree, with the root of the tree being your gallery details. The source list can contain three types of items:
Your gallery home, clicking will display your
gallery details.
An iPhoto folder, clicking on the triangle
to its left will open or close the folder.
An iPhoto album, clicking will display the
album's details.