Greek was the language of international communication in the Roman Empire at the beginning of what we know as the Common Era. Thus, while Jesus likely spoke Aramaic--and may or may not have known Greek himself--the documents of the New Testament (Gospels, letters, and the Revelation) were all composed in Greek.
All English versions and editions of the New Testament are, directly or indirectly, based on the Greek manuscripts of the various books of the New Testament. None of the manuscripts, however, is original--they are all copies of copies of copies and so on. The following text is the first five verses of Luke's narrative of Jesus' birth:
The New Testament canon (the list of included books) was not finally determined until some 300 years after Jesus's death, and only then largely in response to Marcion, who sliced up many of Paul's letters and the Gospels to prove his point about the immediacy of the Spirit of God. The canon includes twenty-seven books: four Gospels, Acts (a narrative account of the early Church's establishment), twenty-one letters from Paul, Peter, James, John, Jude and others, and the Revelation of John.
The earliest pieces were Paul's letters--1 Thessalonians is generally thought to have been the first of the letters we have, and it was written around 48-50 C.E. The Revelation and Acts are often considered the candidates for the latest part, written composed around 100 C.E.
Of the four canonical gospels, Mark is nearly universally considered the earliest, written sometime around 70 C.E.
Click for The Development of the New Testament Canon