Creating a shared calendar in Office 365

Sign into webmail and click to expand all the software available to you on the left.

Give the calendar a name and then press the Enter.

To share the calendar you can Right click on your new calendar and select Share Calendar.
Type the email address of the person you want to share the calendar with in the Share with field.
Using the dropdown menu on the right of the name, choose how much detail you would like them to be able to see.

Click the Send button. This will send the user an email with an invitation to view the calendar.