In order to import images that are already on you machine, please go to the timeline (bitsofMine's main screen) first. There, you should open the app bar and either select "Import items" or "Import folder".
"Import items" allows you to import one or several files from your machine. "Import folder" allows you to import all files from a folder and its subfolders.
BTW you can open the app bar as follows: on a tablet, just swipe from above the screen to the screen; on any other device, just right-click with your mouse above or below the items in the timeline.