In the "Space Admin" area of your wiki you can set the default capabilities of the individuals and/or groups that you would like to have as participants. In most cases, these permissions will be broad, because the nature of a wiki is that you want people associated with your space to be able to contribute as freely as possible. However, you may have specific pages in your wiki space that you do not want certain individuals or groups to view or edit, and for those instances you may want to utilize page level restrictions.
Page Restrictions do not grant access to the wiki
If a user is not granted permission in the Space Permissions, either directly or through a group they are a member of, adding them to Page Restrictions will have no effect.
Adding Page Level Restrictions
Restrictions determine any additional viewing or editing restrictions (above and beyond space level permissions) for that particular page and its children. You can set up restrictions for viewing and for editing.
Accessing the restrictions
You can access the restrictions on a page in two ways.
When viewing the page, choose Restrictions from the Tools menu.
If you are editing the page, near the bottom of every page is a section titled "Restrictions" where you can click on the Edit link.
Editing the restrictions
By default, there are no additional viewing or editing restrictions for any page in your wiki space. This does not mean that anyone in the world can view/edit this page. It means that the individuals and/or groups to whom you gave view/edit permissions in the "Space Admin" area are not currently restricted from viewing or editing this page.
To add an editing restriction, click on the "Restrict editing of this page" radio button; then click Choose me, Choose users (to search for a user), or enter a person's username in the text field, and then click on the Add button. In doing so, you have just restricted the editing of that page to a specific user. Even so, anyone who has space-wide viewing privileges can still view the page (unless, of course, you restrict viewing as well).
The process for restricting viewing is the same, only you would click on the "Restrict viewing of this page" radio button.