New pages my be added to any existing section of your website by logging in to the frontend with Author credentials or higher.  Areas where you can add new pages, will show a small pencil icon next to the word "new". 

After logging-in, you may also click the My Content link from the User Menu on the lower-left of the screen to review a complete list of all the content you've created and add a new content item to any existing section of your website.

Note that after you create a new page from the frontend of your website, you must make sure it is published before others can view it. You can use this feature to save work in progress before it is published.