How to see multiple Calendars in one Calendar view
You can create and use more than one calendar in Outlook. Also, you can open a Calendar shared by other person or even several people (see How to open received calendar), or you can use several Calendars of your own (see How to create a new Calendar in Outlook).
To see two calendars at a time, click the check box next to each calendar name on the Navigation pane:
Outlook shows selected calendars in Side-by-Side view:
To see multiple Calendars in one combined view, click View in Overlay Mode:
Outlook shows selected calendars in one combined view:
To separate calendars, click View in Side-by-Side Mode:
See also this tip in French: Comment afficher plusieurs calendriers dans une seule vue Calendrier.