How to share your calendar with another colleague
Overview
From time to time, it may become necessary to provide additional calendar permissions to another colleague. This can happen if someone needs to manage your calendar, or for other various reasons,
Steps
First, navigate to the Outlook application, and find your calendar in the calendar list under My Calendars.

Then, right-click your calendar, and click the Sharing Permissions option.

Within the properties box, click the Add... button.

The global address list will open, and next you'll search for the user that you want to add, double-click on their name, and then click the OK button to add them.

For this example, I've chose Tyler Burns as the user that I'd like to add.

Once the user has been added, select their permission level, and then click the Apply button at the bottom. In most cases, you'll be providing edit level permission.

Once these steps have been completed, the selected user will be able to edit your calendar.