Step 1: Click on the Calendar button in Outlook
Step 2: Click on your 'Profile Picture' in the top left
Step 3: Click on the 'Settings' Gear Icon next to the calendar you wish to share (NOTE: You can only share calendars that belong to you!)
Step 4: Click on 'Add People'
Step 5: Search for the user you wish to share your calendar with or enter an email address
Step 6: Click on the user you just added
Step 7: Select the Permission you wish to give along with what they are allowed to see (NOTE: This can be changed later)
Step 8: You should now see all the users that have access to your calendar. Here you can change permissions or remove users.