Cloning an Event creates a duplicate copy of the Event... you can edit the new copy without affecting the original.
To Clone any Event, click the green Clone button from the Events tab...
If you already have the Event open, go back to the Events tab by opening the Name drop-down in the upper-right and selecting My Events.
If you're looking to Clone an Event created by another Social Tables user, you'll first need find the Event in your Events dashboard.
If the copied Event does not appear after clicking the Clone button, check to see if it is being blocked by your browser's pop-up blocker. See either the Google Support page, or the Mozilla Support page for more information on pop-up blocker settings. If you're having an issue Cloning an Event that is unrelated to a pop-up blocker, contact firstname.lastname@example.org.