Connect... : this option allows connection to a different PostgreSQL database.
Add new film... : use this option to add a new film to the currently connected database. A dialog box allows you to select a directory name. If the selected directory already exists, then it is updated (see below) ; if it doesn't, the film is added to database, and GPC explores all files in the selected directory to find every image (as recognized by GDK-Pixbuf).
Add new image... : use this option to a add a single image in the current database. A dialog box allows you to select a file name. If the film/directory containing this image is already stored in this database, the selected image is just added to this film ; otherwise, this film is added to the database but only the selected image is referenced in this film.
Delete current image... : when the references of an image are no more necessary, you can remove these informations from database. The corresponding image is not physically deleted from disk.
Update current film... : this option is used to update the currently selected film. This operation will add missing images to current film, update existing images (width and height,...), and remove from database the images which don't exist anymore in the current film directory (if the corresponding option is checked in the "Preferences" dialog).
Print thumbnails... : this option allows you to print thumbnails for the currently selected film ; printing is produced with the help of the Gnome-Print library, which allows you to get previews or directly produce PDF documents.
Print image... : this option allows you to print the currently selected image.
Close... : this option is used to close connection to current database. No operation can be done while database connection is inactive.
Exit : close connection to database and exits GNOME Photo Collector.
P.S. : you can think that adding or updating a film takes too much time. This is due to the fact that GPC (with the help of GDKPixbuf libraries) have to read and load each file in memory, without displaying it on screen, to extract his MIME type and dimensions (height and width).