How to edit a pagel
It's very easy to edit a Wiki page. Simply click on the "Edit this page" link at the top or bottom (also on the sidebar) of a Wiki page to change the page itself, or click on "Discuss this page" link and then on "Edit this page" to write on the corresponding talk page. This will bring you to a page with a text box containing the editable text of that Wiki page.
Then type away, write a short edit summary on the small field below the edit-box and when finished press "Save"! You can also preview your changes before saving if you like. Depending on your system, pressing Enter while the edit box is not active (there is no typing cursor in it) may have the same effect as pressing Save.
It is often more convenient to copy and paste the text first into your favorite text editor, edit and spell check there, and then paste back into the browser to preview. This way, you can also keep a local backup copy of the pages you authored so that you can make changes offline.