To make a certain page visible to only certain users or groups, insert this line of code at the top of the page:
#acl User:read,write,delete,revert,admin All:
In this example, "User" is the username of the user you wish to have the specified access to a page. The same can be applied for a name of a group. The "All:" at the end specifies what the default access is (access for all users). If it is blank, nothing will be seen. Note: admins will have access to all pages regardless of permissions.