J. Gresham Machen (1881–1937) taught New Testament at Princeton Theological Seminary. He wrote this book for students starting Greek with no background, and it is still used today. Its lessons teach Koine Greek forms and grammar step by step, with exercises in both directions and vocabulary drawn from the New Testament.
This is Koine Greek, the common Greek of the first century. It is close to, but not the same as, the Homeric Greek of the Iliad and Odyssey and the Attic Greek of Athens. The site's Greek alphabet page, flashcards and Gospel reader are all Koine too.