Copy event makes a new event from an old one. It is in the event page's Actions menu, and in each event's menu on your Events page.
The copy brings the title, the place, the notes, the look, the photo, the date and everyone who was invited, whatever they answered. When the original has already happened, the date moves to the same weekday and time in the next week to come. Check it, remove anyone who shouldn't get this one, and send.
The copy doesn't bring the end time, repeats, plus-ones, who sees the guest list, or public replies. Set those again under More.
New event keeps what you type in this browser as you go. If you leave and come back, the form starts empty with one line about the draft you left, and Continue brings it back or Discard throws it away.
Save draft is different: it saves the event to your account and sends nothing. It shows on your Events page under Drafts as Not sent yet. Continue opens it to finish, and its event page has a Send button.