By default, the iCal comes with the event name and date. If that's not enough, you can add a description too. Here's how to do it.

Go to your event menu and select Details and then Edit Details.

Scroll down to the Event automated emails section and add your iCal description.

Once you're done, scroll down and click Save Details.

The description will show on all iCal links - Thank you page (dependent on template), booking confirmation and event marketing emails.