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Click +Add Content, click New Folder.
Name your folder and input Display Name and Title. (Refer to Filenames, Titles and Display Names for more information.)
Make sure the placement of this new folder is in the Gallery folder you created. Click Submit.
The structure of your folders should look like the example below:
Move the Gallery Block into the images folder you just created. This folder will hold your gallery images as well as the gallery block.
To add images to your folder, go to +Add Content, then click Upload a File. If you upload only one image, the Title will automatically fill with the name of the image. If you bulk upload, the Title is not needed. Make sure the Placement Folder is the images folder you created above.
The uploaded images show at the bottom. Click Submit.
The final folder structure should look like the example below:
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