Close, the last of the four sections on a deal's Deal Info tab, records what actually happened at closing.
Fill in Actual Closing Date and Actual Closing Price. Actual Closing Price is its own field, blank until you fill it in — it's independent from Contract Price (on Contract Facts) and from Projected Sale Price (on Disposition Details); nothing else on the deal ever fills it in for you. Once both Close fields are filled in on a deal that isn't already closed, a dialog reading "Mark deal as Closed?" offers to set the deal's status to Closed for you. Select Yes, Close Deal and everything you entered saves immediately — there's nothing else to press. Select Not Yet to keep the values pending instead, then select Save Changes when you're ready to apply them.
Actual Closing Date is the day the deal really closed, so it starts out blank — the planned date you enter when you create a deal is saved as its Original Closing Date (on Contract Facts) instead. If you mark a deal Closed or Funded while Actual Closing Date is still blank, TED fills it in with the day you closed it (your team's time zone). A date you typed yourself is never replaced, and moving a deal back out of Closed keeps it.
Once a deal is closed, this section shows a Closed label next to its header.
Canceling a deal instead of closing it works differently — see The deal header for the status dropdown, the required cancellation reason, and who caused it.