You can manage the page restrictions by clicking on the padlock 

1. You can restrict viewing and/or restrict editing
2. You can select a person
3. or a group

1. Select the type of restriction you want to do
2. Enter the person or the group 

Click  and 

The padlock is now closed and red. It means that there is applied

You can display and manage restriction by clicking on  (no need to edit the page)