This is the Membership Options Page for this demo.
What is the Membership Options Page in s2Member?
It's a Page you create in WordPress (like any other Page) and then you designate it as your Membership Options Page when configuring s2Member. This is the page users will see if they attempt to access an area of the site that is currently off-limits to them.
While not required, most site owners will also use this page to list details about the products/services they offer. It's a great place to show a list of prices, and you can provide a list of links that lead to checkout forms that you've constructed using s2Member Pro-Form shortcodes.
See: Dashboard → s2Member → General Options → Membership Options Page
See also: [s2MOP /] Shortcode Documentation
Tip: You can use plugins like Responsive Pricing Tables to generate your own set of options. The above pricing table was generated with that plugin, and there is a lot more you can do.