A shared mailbox is an email account that multiple users can access and use to send and receive emails from a common address, such as "info@company.com" or "support@company.com", without requiring individual usernames or passwords. To open a shared mailbox in Outlook on the web,

Sign in to Outlook on the web: Access your Outlook account through the web browser.

Click your name: Locate your name or profile icon on the navigation bar and click it. Select "Open another mailbox": A list will appear, choose the option to open another mailbox.

Select "Open another mailbox": A list will appear, choose the option to open another mailbox.

Type the email address: Enter the email address of the shared mailbox you want to open (in my example it's our IT Support shared mailbox), then click on it

 Click "Open": A new Outlook on the web session will open in a separate window, allowing access to the shared mailbox.