Here you can digest how to use Wikipedia in bite-sized morsels. The tips listed below were created for the Tip of the day project, or the Styletips project, but are listed here by title and organized by subject area for your convenience.
Wikipedia has index pages called Categories, in which links to articles are provided based on category tags included in each article.
To add an article to a particular category, add [[Category:Category name]] to the article's text (preferably at the bottom). The assigned category should now show up at the bottom of the article, and a link to the page should show up on the indicated category page in Wikipedia's category system. If the category shows up as a blue link it is an active category; if the link shows up red then the category has yet to be created. Click on the red link to create the category page.