Adding your photos to your poster is very easy. You can double click on the cell and a dialog will open allowing you to select the pictures you want. You can select more than one, and if you do each additional photo will be added to the next visible cell. You can access this dialog from the toolbar button and the main menu as well as the right click menu for the cell.
Another way to add photos to your poster is to simply drag them in from Windows Explorer from where they reside on your local drive. If more than one photo is dropped onto the poster each available cell after it will store the next picture that was dropped.
You can drag a folder to a cell and it will add all the images in that folder to your poster. This does include images in subfolders as well.
When you add photos to your poster the images will be added to the library window. To display the window shown above click on View|Poster Thumbnails. If you want to have quick access to photos on your local drive you can drag them to the library window and they will be stored with your poster so you can quickly access them the next time you open the poster.
After you have added your photos you can move them around to position them where you want.