To share calendars, you need to be using Outlook with Exchange Server. You can tell if you're using Exchange Server by viewing your e-mail account. If the account type is Exchange, as shown in the picture, you're using Exchange Server. If you're not sure what kind of e-mail server you're using, ask your systems administrator or office computer expert.
You cannot share a calendar unless you are keeping it on the server. A calendar stored on your own computer, in a local PST file, can't be shared. For more information about PST files, see the course "File or archive your e-mail on your own computer."