How can I view a calendar that includes other user's activities?

How can I view a calendar that includes other user's activities?

A user can view the activities listed in another user's calendar based on the roles and hierarchy. 

For example: 

  1. The CEO can view all the records but the sales manager can view only the records of his sub-ordinates. The sales manager cannot view the CEO's records. 
  2. Two sales managers can view each others' records only if the Share Data with Peers check box is selected for a role.