Initialy the 'Restore' button is not accessible because you have not selected any backup to restore.
With the ABE you can create as many backups as you need. All made backups are listed at the Backups page of the main ABE window. To restore a particular backup, please, select the one in this list. The 'Restore' button on the ToolBar now becomes enabled. Press this button or use the 'Restore' item of the 'Backup' menu.
If you want to restore the last created backup, please, select the 'Restore last' item of the 'Backup' menu.
To restore a particular file within any backup, please, double-click the backup, right-click the file in the file-list appeared and select the 'Restore' item of the popup menu.