Linux Journal publishes articles on all levels of developing and using Linux and the software that runs on it, including everything from how to write device drivers to how to edit photos with The Gimp.
Most articles are fairly technical, and it helps to have a working knowledge of C to get the most out of it. Linux Journal does run some user-level and business articles in every issue, and sections called Up Front and EOF tend to be less technical. The Linux Journal web site has some of the articles from the printed magazine, but most of the content on the site is a separate webzine.
SSC also publishes the webzines Linux Gazette.