To add pictures in the gallery you have to upload them into the folder called "pictures". There you can also add folders, where you can add more pictures.
All the pictures you add the the "pictures" folder will show in the gallery as tumbnails, and the folders you make will be like sub-gallerys.
In my gallery i have no pictures in the first folder only in subfolders.
So the adress for a picture in the first gallery folder is like this:
#removed_broken_linkpictures/picture.jpg
And in subgallery like this:
/pictures/subgallery/photo.jpg
look only where it's red to locate the folders you need to think about.