How to add categories to content I'm still new to Drupal 7. I've read a couple of things on how Drupal works, but I don't quite get some things though. 

How do I create articles for different categories? I would like to make articles that can be listed under graphics, painting, or 3D etc. How can I categorize them in the main menus? How different is this to the blogging module or book module? 

I know this may have been posted similarly here, but I would just want a simple explanation not found in long chapters. Thanks guys.
You're probably looking for taxonomy. Create a vocabulary and name it something like "categories". Add terms for each category you want like graphics,3D,ect. Then just add links in your navigation menu. Under your content type, add a term reference field and choose your "categories" vocabulary. That way your users can choose a category when they submit something.