Here, just knowing the Greek alphabet won't help much - unless you know the Greek words for "arrivals" and "departures". On the other hand, since virtually everything is in English as well, you won't even need to read the Greek... with one exception. The English says "to taxis" but the Greek above adds an important bit of information. Can you see what it is? Look at the word "Metpo". If you know your alphabet, you know that "P" is an "R" and that the directions in Greek include the information that you go in the same direction to get on the "METRO", something omitted in the "translation". Knowing your letters just saved you some time and trouble.
Larger airports in Greece usually have signage in Greek and in English.
This Step-by-Step is designed to use in conjunction with my "Learn the Greek Alphabet" series. You have your choice of visiting the start page for that, or to sign up for a daily email e-course with each three-minute lesson once a day for eight days. (Of course, you also have the choice of doing neither, but we won't talk about that option.)
Learn More Greek:
Learn to Say Hello in Greek