[header] How to check in for a flight on the delta airlines mobile app [title] Sign up for a delta skymiles account well before your flight. [step] By doing this on the delta website, you'll essentially be opening up your delta skymiles account. You'll get to check in by connecting your flights later. 
[title] Connect your airline reservation to delta (for delta flights only). [step] Do this if the flight ticket was booked under another company or method.