Click on Calendar (top of screen).
The Calendar toolbar (on the far right of screen):
Listed underneath will be all the calendars that you currently have shared access to.
Calendar view options
(All the screenshots below are in thumbnail view, click on those you wish to see more clearly.)
Looking at your own calendar, you will see there are a few view options to help you. In the following screenshots we have added a number of appointments to show how they appear in the different views.
If an appointment has been sent to a number of recipients, you can click on the appointment (see cursor position in screenshot) when it is in your reading pane to see a quick view of the number of replies. Clicking on the blue text list of Accepted...etc on the popup, will open another view to see actually who has accepted/declined etc.
Please Note: If a recipient has accepted a meeting but chosen to not send a response - then they will appear under the 'No response' category.
There are other views available if you are using the Outlook client - Schedule view and variants to the Month view. For other options in the Outlook Web App, see viewing multiple calendars.