Numbering your masks will help keep track of what images you want, and where you want to put them. This is essential with filling from Bridge.
Make sure you select all of the layers that you want to have filled.
After selecting your boxes you would like fill, click "Number Masks" on the Album Builder Panel.
Now you have your boxes filled with number for easy filling! This is important when filling from Bridge. Then you know the order in which the images will fill.