Shared mailboxes are the easiest way to setup a centralised mailbox for multiple people.
In the office 365 Admin centre, go to Groups, Shared mailboxes and Add a shared mailbox. Once setup you can edit permissions, setup forwarding, allow it to be shown in the address lists etc.
You can access the mailbox using the following URL format:
https://outlook.office.com/mail/[email protected]
You can also add the mailbox to your OWA by right clicking on folders and clicking Add shared folder
In Outlook, the shared folder should appear after some time for the user once added into the mailbox permissions. If it doesnt you can follow these steps:
Open Outlook.
Choose the File tab in the ribbon.
Choose Account Settings, then select Account Settings from the menu.
Select the Email tab.
Make sure the correct account is highlighted, then choose Change.
Choose More Settings > Advanced > Add.
Type the shared email address, such as [email protected].
Choose OK > OK.
Choose Next > Finish > Close.