Many times, I do see people who want to share their Outlook calendar with their colleagues but don't know how to achieve this.
Click your secondary mouse button on the calendar icon in the lower left part of Outlook and select "Options...":
In the Calendar Options dialog, click the "Free/Busy Options..." button:
The now open Calendar Properties dialog lets you switch from "Free/Busy time" to the "Free/Busy time, subject, location" or even the "Full Details" permission:
Please note: if you want to have appointments that nobody but you can see, you should flag this appointment as "Private". If you have chosen "Full Details", others are able to see details of private appointments as well.
The "Private" icon is not visible in a smaller window size. So make sure that you maximize the window in order to see "Private" beneath "Categorize", "High Importance", and "Low Importance" in the ribbon bar.