When you create a New Page Group, you'll be the only who can see it. To make it visible to others you need to share it. Sharing a Page Group happens by sharing directly with users, sharing with groups or publishing a Page to the whole organisation.
In edit mode, select Page Group settings from the right-hand navigation. From here you can see the "Share page group" section. In this section you can first add a user and then select the user role (Editor/Viewer).
Pages cannot be shared per Page. When you share a page group editors will have edit rights to all the pages inside the page group.
Only Page Editors can see unpublished pages.