By default all the primary calendars are shared with view access to other users. Users can add these calendars to their own calendar view for fast access.
- Open Google Calendar
- Click the +-icon next to "Other calendars" and click Subscribe to calendar
- Type in the user's name or address and press and click on the user's contact box from the suggestions
- The calendar gets added to your "Other calendars" from where you can toggle its visibility on and off by clicking the name
You can also check other peoples calendars from the "Meet with..." box without subscribing to their calendars. Just start typing their name on the field and click their name when it appears on the suggestions. Their events will pop up to your calendar view and you can easily check when they're free or busy.