When you are logged on to the site, and you have editor or administrator permissions, you can edit the static webpages on the site, add new web pages, and delete web pages.
When viewing a page, you can edit that page by pressing the little “Edit” button in the lower left corner of the page:
To add or remove pages etc., go to the “Pages” menu item in the administration interface for the website (the “Dashboard”):
For more info, check out the WordPress documentation for Pages.