That was a long process, during a few centuries. One of the most important requirements was that a book was only accepted if it had an apostolic origin. This should not be interpreted too strict however. forex signals

Some books were written by an apostle himself: Matthew; John; I, II and III John, a few letters of Paul, I and II Peter and Revelation. James and Jude were both (half-)brothers of Jezus and had an important role in the early church (James together with the apostles John and Peter in Jerusalem). The letter of Jude is strongly connected to II Peter (which was written earlier) and often refers back to it. Read both letters and you will see the relation, which makes the letter of Jude closely connected to the teachings of the apostle Peter.

Many others were accepted because they were written in close connection or on authority of an apostle. Mark has been co-worker of Paul for a while, and has done much together with Peter. It is on account of Peter that the book of Mark was written, and (later on) accepted in the New Testament. Luke was a co-worker of Paul, and his books (Luke and Acts) were strongly connected to Peter and Paul. In fact, in Acts these two apostles are the central acting persons.

Paul often only dictated the letter one of his secretaries/co-workers and only wrote the closing greeting as a sign that the letter was written by on his authority. Examples are: Rom. (see 16,22); I Cor. (see 16,21); Col. (see 4,18); II Thess. (see 3,17); Philemon (1,19).
Of II Cor. 13,10 Paul says that he writes the letter. This must however also be understood as "writing by means of a secratary", which was quite usual that time. The same applies to Ephesians, Philippians, 1 Thessalonians.
Some are unsure (I Tim., II Tim., Tit.): either written by Paul himself or by a secretary.
When writing to the Galatian assemblies, he was hurrying so much that he wrote the whole letter himself: Gal. 6,11.

Hebrews was accepted as book of the New Testament on the assumption that it was written by Paul himself. That has turned out to be wrong. It has been one of his pupils who has written the book. It is unknown whether Paul new of this book or not. It is nevertheless very Pauline in the sense that his influence is apparent. But we must admit that, had it been well-known that Hebrews is not written by Paul, it would probably not have been part of the New Testament nowadays, except for the case that it was written in close connection to Paul, but that is impossible to verify. Therefore, we do better keep it in our bibles.