CarolA is correct.
However, if you only have carryons, online check-in can be a worthwhile way to save time at the airport. I've done it twice. You actually print out your boarding pass on your own printer.
Be aware, though, that you must make sure each passenger has a Skymiles number and that the number is attached to each passenger's reservation. Then you must log into each Skymiles account on the Delta web site and print each boarding pass separately.
We had problems both times we used this because my husband and I had booked a flight together and only his Skymiles number was put on the reservation. Therefore we couldn't print out my boarding pass. However, I e-mailed the Skymiles online help people and they were able to add my Skymiles number to my ticket each time. Unfortunately the people on the phone couldn't seem to do this. They didn't really understand why you needed the passenger's individual Skymiles number on each ticket, or how to do it.
By the way, both times we ended up with boarding passes that did not seat us together, and we had to get this straightened out at the gate (luckily this was no problem). So online check-in has its problems. However, it did allow us to bypass the big check-in line and get directly in the Security line to go to the gates, which probably saved us an hour in line.
Mary
MouseSavers.com