Here you can select what groups should have access to the page by selecting them below the field Available Items, so that they are added to the field Selected Items.
If the page should be accessed by all groups you can just select the group Show at any login.
It is also possible to hide pages when you login, to create more space in the menus. Use the group Hide at login for this.
Finally it is possible to extend the access settings to all subpages by enabling the checkbox. (img. 2.1.1)