Editing pages can be done by going to the editor tab (next to the viewer tab). Wixi uses the txt2tags markup language, so learning the basic first is very usefull. After you have edit the contents you may add a comment and save the page.
[Link to a page AnotherPage.html]
[Link to website http://www.slashdot.org]
[Link to a file file://home/johndoe/somefile.txt]