To share a calendar in Microsoft Outlook, follow these steps:

Outlook Desktop:

1. Click on the "Share Calendar" icon in the home menu of your Outlook calendar.
2. Select the contact you wish to share your calendar with.
3. Click the "Add" button and then pick from your address book to send an invitation to share your calendar.
4. Once the contact is added to the list of shared calendar contacts, you can change their permission level. To allow them to edit events, set the permission level to "Can Edit".

Outlook Web:

1. Click on the three dots next to the calendar in the calendar view and select "Sharing and permissions".
2. Enter the name of the person you want to share your calendar with.
3. Click the share button.
4. Set the permission level to "Can edit" to allow the person to make changes to events.

Remember, only people in your Outlook contacts list for the account you have logged into will appear in the list for sharing​​.