From and Calendar view, right click on the appointment, select Label from the pop-up menu (see thumbnail below) and then select the color and label you would like to use.
From the appointment form, select a label from the Label drop down field in the upper right hand corner of the …
First switch to the Calendar folder and then on the Outlook Edit menu, select Label and the Edit labels from the sub menus (see thumbnail below).
The Edit Calendar Labels window will open (see thumbnail below). Type in what ever text you want to use for each label and then …