Help:Adding A Page
Roughly, follow this procedure:
Find a page you want to link from, edit it, and put the desired page name in link brackets e.g.
[[My New Page Title]]
Think about the title as it will appear on the page itself, not as it should be in a link. If you want to change the link text, you can do so by separating it from the title with a pipe (|) character, e.g.
[[My New Page Title|Link to my new page]]
Now when you reload that page, you should see a red link to your new page. Click on it, and you will be editing your new page.
Put in whatever content you want.
When you're done, consider adding it to a category (or categories), so that it'll play nicely with the rest of the site. If it's a new category, you might want to consider updating the Breadcrumbs file. And you might conceivably want to add it to any of the menus.