It provides a system of receipts to monitor the movement of mail from acceptance to delivery.
Optional insurance is extra.
You cannot use it with regular envelopes. Attach a standard US Postal red Label 200 containing a registering number to the mail piece above the delivery address and to the left of the postage. Print your postage as usual. You will notice that a single stamp for the full cost of mailing, including Registered Mail, is printed. Bring the mail piece to the Post Office for mailing.