A redirect is a page which redirects a user to another page. It's helpful when a page has more possible titles. You get also a redirect when you rename an article.
If you want to redirect a page you simply have to clear the page and add this code to the page:
#REDIRECT[[Pagenameyouwanttodirectothere]]. Make sure the redirect code is on the top of the page. All other information on the page will be ignored, except categories. Don't forget to save the page.
If you want to change the redirect, go to the page which redirects and click on edit to edit.
It's possible there's a double-redirect; this means the redirect page redirects to another redirect page. To redirect the first redirect page directly to the page you want you only have to go to the redirect and edit it.