Imagine this: you start clicking on events in your Google Calendar and accidentally delete that Super Important Meeting. Now what?
Take a deep breath, and remind yourself that Google never deletes anything. Restoring your deleted event is just a few clicks away. If you see a pop-up in the top center of your screen that reads "Event Deleted" you can click on the "Undo" link.
If that option is not visible, simply go to your Google Calendar's Trash folder, by clicking on the the drop-down menu next to your calendar. Next click on "Trash" and click on the item you want to restore. This menu can be a little tricky to find, but it might save you some grief! If you're a visual learner, check out this screencast of an event that was accidentally deleted and restored.