Outlook stores everything in folders. This includes calendar entries. So, to create an additional calendar, you would first create a new folder in which to store items for the new calendar. As shown in the picture, this can be done easily by clicking the File menu, pointing to New, and clicking Calendar. From there you use the Create New Folder dialog box and fill in the details for the new folder (here we've named it Family and made it a subfolder of the main calendar). Once you create that calendar, you will see it listed under My Calendars.