Go to the page you would like to restrict. From the Tools drop down menu, select Restrictions.
In the popup window, select to either Restrict Viewing or Restrict editing or both.
Type in the user or group name you wish to have view or edit the page.
Or you can select yourself by pressing the Me button.
After making your selections you still have the option to Remove restriction. You can always come back at a later date to remove any restrictions you have in place.
When finished making your selection, press Save to finalise your selections.
Please note that you may need to update the parent page, please see the screen dump below: