A shared mailbox is an inbox that allows multiple people to send and receive email from the same address. This is great for a company that might want to share the load of responding to customer inquiries, for example. Any member of the shared mailbox may respond to an email sent to the shared address. And any response will appear as if sent from the shared mailbox address, rather than the individual person.
Say Molly sets up questions@mollysbarkandwine.com, and adds her partners, Jane and Paul, as members. Whenever any of the three reply to a questions@ email, the response will come from questions@mollysbarkandwine.com, instead of from Molly, Jane, or Paul’s individual email addresses.
Because a shared mailbox is an entire inbox, the members have a common calendar, and contacts list. A shared mailbox allows a certain amount of email storage, without needing to pay more.
A shared mailbox technically has no owner, and it doesn't have its own password. So, members aren't able to log in to the shared mailbox, directly. The admin has to add you as a member of the shared mailbox, and then you can access it, either online or through an email client.