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You need to set xcgal group permissions to who can upload, etc then you will have to create a category/album before you can upload. As above post you can upload via the front end by clicking on Upload Picture link in the module front end, user side.
You can also batch upload by ftp'ing a folder of pictures into the xcgal/albums directory then select Batch Add Pictures from xcgal admin - ensure the folder you upload is chmod to 777.