Here's what the various fields mean on the add and edit field pages. Most of it's pretty self-explanatory, but there's a few things that you can still learn.
This value is used internally to help you identify the page and as the menu item label.
This is the heading that appears on the page.
PHP, HTML or Smarty. This determines what kind of content type you enter into the page. HTML is the simplest, but PHP and Smarty give you far more control over the content of the page, as well as giving you access to the database and anything else server-side.
The actual page content.
Who can access?
This provides a secure way to protect the page from being accessed by anyone in particular. However, as the comment notes: pages still need to be assigned to a client via their menu or a hardcoded link in order to be seen. This setting is for security purposes only.