The main information you have to enter to the ABE project is what files you wish to backup.
Within ABE you can use two lists of the masks for this purpose: Included masks and Excluded masks.
A file is counted as included if and only if it matches to at least one included mask and does not match to any excluded mask.
You can add / modify / remove masks of these lists on a project creation with New Project Wizard as well as later with items of the Mask menu.
When you are about to add or modify as included as excluded mask the Select Mask window helps you to do this. Within this window you have to select a mask folder and a mask filter. Manually typed filters can be saved for later use without retyping it again. You can enter multiple wildcards into one filter by dividing each other with ';' (semicolon). ABE contains very flexible facility - the Filter Organizer - to control all aspects of filters. Use the Include Subfolders option to define the ABE behavior regarding subfolders of the mask folder.
When you return from Select Mask window, you can see the newly selected mask in the corresponding masks list.
You need a least one included mask to enable the Create Backup command.
The excluded mask list may be empty, if you don't need to exclude any files.