Are you in the left hand column navigation area that looks something like the following?
If so, click the Pages or Content button/link at the top of the page:
Use these buttons to navigate around your site instead of the left column. In the main area of your screen, you should now see the button.
If you are not in the left column navigation and are still having issues, please email email@example.com with a screenshot of what you are seeing. This may be due to insufficient user permissions and will need to be looked at on a case-by-case basis.