To load photos in to PhotoInfoEditor just click the 'Load Pictures' button in the bottom left-hand corner. In the 'sheet' that appears (a standard Mac file-open window) select either a folder of files that are to be loaded, or a single file.

Using PhotoInfoEditor it is possible to load multiple files from different sources and then combine them into a final folder when they are saved.

To remove a picture from the loaded list of photos just click on the photo file name to select it and then click 'Remove Picture' button.

Next... adding meta-data