When using Simple Permissions you can can use Site Access.

Viewing Permissions

This is the base permission level, most sites will want to be "Public" to allow users to see them without having to login to the site.
You can adjust the Viewing permissions by changing the selected Radio box, Public is the default selction.

• Public - Anyone may view the website.
• Members Only - Only registered users may view the website. 
• Private - Only the administrative group may view the website.

Edit Access

This section allows you to define who can edit the site. Changes made here can be overwritten on each page.
Adding a group to this section will add them as an option to the "Permissions" option for each page. Multiple groups can be selected to edit the site. Remember explore advanced permissions if you need more granular control.