property Calendar.Events as Events
Retrieves the control date events collection.

TypeDescription
Events An Events collection that contains Event objects. Each Event defines a DATE and its graphical information like: foreground color, background color, font attributes, tooltips, images and so on.

Use the Events property to access the Event objects. 

The following sample applies a bold effect to "yesterday" date:

Calendar1.Events.Add(Date - 1).Bold = True