Open your favorite web browser and go to office.com and click on "Sing-in"
Another window will open, enter your email and password
If you have two factor authentication enabled, you will have to approve the request using the Microsoft Authenticator (Optional)
Once you are logged in, locate the Outlook icon and click on it
Inside of your mailbox, RIGHT click on "Folders" and then click on "Add shared folder"
A windows will open, type the email address for the shared mailbox and click on "Add"
You now have the shared mailbox. Just click on the arrow and click on inbox to see new emails
Enjoy!