The first option there, “Get Info,” will open a separate, detailed window for the event you right-clicked on.
The neat thing about that window is that it won’t go away until you click the “X” at the upper-left corner to dismiss it; this is useful if you want to compare events from different months, for example, because you can open multiple “Get Info” windows at once.
Not sure why I’d need to compare those two events, but whatever.
The second choice on that right-click menu, “Calendar,” is probably my favorite. It’ll let you quickly swap your selected event to a different color-coded calendar.
The next few options on the contextual menu (“Delete,” “Cut,” “Copy,” “Paste,” and “Duplicate”) should be pretty self-explanatory, but they’re still handy. Choosing “Copy,” say, will let you go to a different date or time and right-click to paste the event.
This’ll save a ton of time over re-creating the item from scratch, especially if you’ve set some custom alarms, added in locations, or what have you. Just so you know, however, I much prefer Option-dragging events to duplicate them.
Nothing against the contextual menu, you understand—especially for those of you who don’t like remembering keyboard shortcuts—but that method is just faster. And cooler, somehow.
Anyway, the last three menu choices you have all relate to sharing details with other people.
If you’ve invited people to an appointment, “Email All Invitees” and “Message All Invitees” are good to know about, as those’d allow you to get in touch with specific folks quickly. But that “Mail Event” option is incredibly, indubitably awesome. It will automatically compose an email with the details of the event you right-clicked on, plus it’ll attach a little .ics file that your recipient can double-click to add the event to his own calendar.
You wanna look like a wizard when you send the family reunion details to your Aunt Mildred? That’s how you do it. Just don’t be surprised when everyone starts asking you for tech support afterward.