Open your web browser and navigate to office.com 
Type your username and password
Locate the Outlook icon on the left side of the screen
Once in outlook, select the Calendar icon from the left bottom of the screen
On the new window, find Calendar under My calendars and click on the three dots. From there select Sharing and permissions and click on it
Type the name of the person you want to provide the edit or review access and select the users from the list
Select Can edit and click on it, then click on Share
No close that windows using the X on the screen. (make sure the user is listed before you close the window)
Happy Sharing!