I switch to user mode, and I tried to create my own gallery or upload a file, but, I couldn't. How do I create a user gallery? Users (registered) are allowed to have them, I checked the permissions.
Since I can't edit my topic, might as well reply.
I cannot create an album into the category for user galleries, even as an admin.
Both issues you mention differ: user mode is not meant to show you what regular users can do (permissions-wise). Read the docs (http://coppermine-gallery.net/demo/cpg14x/docs/index.htm#admin_user_mode) to find out what the admin-mode/user-mode toggle is meant to be used for. Log out as admin and log in as user to see what regular users can do.
You (as admin) can create a user gallery of your own using the "*my gallery*" category. Again: please read the docs.