Upon initially visiting the node gallery relationships page, you'll be presented with something resembling the following:

A relationship is what associates a gallery node type to its image node type. Each relationship consists of a descriptive name, a gallery content type, a node content type, and settings that apply only to that relationship.

Content types belong to one Node Gallery relationship exclusively -- every image type has exactly one gallery type and vice-versa. This dependency may be removed in later development, see http://drupal.org/node/1130450.

If you click Change settings, you'll be presented with the following:

Relationship settings: Here you can specify a name of your choice, and if you have more than one imagefield attached to the Node Gallery image content type, you can change which field the module uses via the dropdown here.

Gallery settings: You may change settings which apply when viewing a gallery as a whole here. You can select the view to be used to display a gallery's images in both the full-page view and the teaser view here. Also, you can specify a view to use as the default sort query. If you can represent your desired sort in a view, then Node Gallery can support it!

Image view settings: The settings here pertain to behaviors used when displaying an individual image within a gallery. You can elect to disable the image navigator completely (to move it, see content type settings). When "Use named anchors..." is selected, when a user clicks a link on the image navigator, the page will jump down to the top of the next image -- eliminating the need for the user to scroll down to view the full image.

Manage images tab settings: These settings pertain to the "Manage Images" tab displayed when viewing a gallery node. You can place a checkbox next to every field you wish to display on the tab, specify the maximum number of images to display per page, enable/disable the dropdown that allows changing the gallery that an image belongs to, and even allow basic image rotation from the page.