The easiest way to track a Delta Airlines flight while it's still in flight is to use a flight search program such as FlightAware.com. By inputting the airline flight number and the departure and arrival cities, you learn exactly where the plane is and the estimated landing time. If the plane is already on the ground, the program tells you the time of landing, the exact mileage of the flight and the average altitude flown.
If you only know the departure and arrival airports, but not the flight number, pull up the departure or arrival airport, and look for a flight that matches the time frame you're expecting. It's usually easier to use the Arrivals and Departure lists rather than the airport map.
Look for DAL, which is the airline flying code for Delta. If a flight looks familiar, click on the flight number to pull up flight details. If you've got the wrong flight, just back up to the previous page, and try again.
If you prefer, and if it's close to the plane's scheduled take-off time, pull up the departure airport, and try to find the plane on the map. An orange and white square on the lower right corner lets you enlarge the map, which is handy at busy airports like LAX or SFO. Put your cursor over a plane to find the flight number; if it's a DAL flight, click on the plane to pull up the information box. If you've got the wrong plane, try again. This also works for arrival airports.
Arrival flights are in blue, departing flights are green and planes flying in the airport's air space but not landing are pink. The larger planes on the map represent larger planes in real life.