Create a "Link" between two collections

I have two collections one for the Users, another for the Wallpapers. The first has default FF fields, the second fileds related to uploaded images (wallpapers for smartphones).

When an User uploads a file it'll be stored inside Wallpapers collection and I'd like to create the same field for User Collection (display_name) and Author field inside Wallpapers collection as well.

I guess I need to use "doc reference" function but how?

The problrm is also when an user edits his profile, the "author" field of Wallpapers collection should update automatically. Otherwise when I'll filter the wallpapers as well the will not be shown.

thanks

SOLVED: I made also a connection between two pages by transfering the parameter, UserID. This works even in the socond page!