If you are allowed to edit pages in this Site, simply click on edit button at the bottom of the page. This will open an editor with a toolbar pallette with options.
To create a link to a new page, use syntax: [[[new page name]]] or [[[new page name | text to display]]]. Follow the link (which should have a different color if page does not exist) and create a new page and edit it!
Please back-link pages that you create using the "+options" button at the bottom and setting the parent to the parent page!
Although creating and editing pages is easy, there are a lot more options that allows creating powerful sites. Please visit Documentation pages to learn more.