Here are the pages I've been using the most to guide me in using Wikipedia properly. Browsing through these you should be able to find all the answers to questions about changing pages or adding content. Don't forget you can also use the discussion tabs to ask questions of other users.
http://en.wikipedia.org/wiki/Help:Contents -- This the most important page, the help menu. Many of the pages here are all linked together, so you might run into the same one over and over again. Use the menu to narrow down your search.
http://en.wikipedia.org/wiki/Wikipedia:Contributing_to_Wikipedia -- This is just the general page on all of the different ways to work on Wikipedia.
http://meta.wikimedia.org/wiki/Help:Wiki_markup_examples -- The page on how to make your article look and work right.
more to come soon...