Mainly for ourselves, because we never remember how it goes, here's an instruction on how to create a gallery on freeflux accounts:
Best create a folder on your computer with the pictures you want to upload and zip it. The zip file must be no larger than 20 megabyte.
In your freeflux admin click on the "gallery" folder in the folder tree on the left, then on "create new gallery" in the right hand frame under "collection". Type the name you want for the gallery and the folder with this name will appear in the folder tree on the left.
Click on the folder just created and click on "upload multiple images in a zip" and choose your zipped pictures folder. The pictures will go to the folder you created and selected before.
Once your images appear in the folder in your folder tree, click on the image files and choose "Edit properties". Here you can add title, description and tags to your gallery pictures. Thats it.