The program should refuse to add a file more than once, so if an image is appearing multiple times, then either the duplicate thumbnails represent different files, or one or more of the thumbnails is disconnected from its original, and should be deleted.
The disconnected thumbnails will appear with a red icon along the bottom of the thumb. If you zoom in all the way to a disconnected image, you'll see a message about how the program is searching for the file. If you have multiple instances of that image in Starter Edition, just hit Cancel, then click on the thumbnail, then click the delete button.
In the future, don't use the 'Get files from folder' command to add files to Starter Edition; instead, use the File>Get Photos>From Favorites command to indicate a folder where you will add any new files to your computer; then when you add any NEW files to that folder you indicate there, it will automatically be added, and it won't waste time trying to add duplicate versions of files.