After you read this, you probably want to read the Implementors' Guide to Internet Calendaring currently being drafted by the IETF Calendaring and Scheduling working group. Alternatively, you may wish to follow some of the pointers in this document to various parts of the iCalendar RFC(s). It's up to you. If you want to grok iCalendar in fullness, however, you will have to inhale the RFCs at some point.