Do I have to register on this site to have full read access to all the content?

No, there is no registration necessary for the main site. If you want to contribute, use our forum. There you must register. Go to http://mw3d.org/forum

I want to write articles on your site, how can i do this?

First, write some articles in our forum. If you still think your articles should be placed on the main site, contact us, and we'll talk about that