In order to access a shared mailbox for which you are an editor or viewer in Outlook for Windows follow the steps below.
Open a Shared Mailbox
In the folder navigation window on the left side of Outlook, scroll down past your individual mailbox to find any additional mailboxes that you have access to. If you have been granted access to a mailbox, but do not see it in the listing, follow the steps below to "Add a Shared Mailbox."
If your access was only recently granted, you may need to close and restart Outlook before it becomes available to you.
Add a Shared Mailbox
Navigate to File>Info>Account Settings > Account Settings
Select the user's email account and click "change" on the bar above the account. (If the user has 2 accounts, the account that has permissions to use the shared mailbox should be selected).
Click on "More Settings..." in the lower right hand corner of the window.
Navigate to the "Advanced" tab and then click the "Add" button in the "Mailboxes" field.
In order to find the correct mailbox to place in the "Add Mailbox" field, 1 of 2 methods can be used:
(Easier) Type in the actual email address of the shared mailbox (i.e. firstname.lastname@example.org) and then click "OK".
Type in the name of the shared mailbox starting with an asterisk (i.e. *HD Student) and then click "OK".
Close all of the Account Settings windows and make sure the shared mailbox shows up as an inbox on the left side of Mail in Outlook.