How does a book get to be in the Canon of Scripture?

How does a book get to be in the Canon of Scripture?  Who decides?

Well, if you’re looking to get a book into the Bible, you’re too late!
The Canon of the Bible was closed in the first century of the Church.
Who made the decisions?  In the first century after Christ, rabbis in
Palestine gathered to form the canon of the Hebrew Scriptures (the Old
Testament). They selected only those thirty-nine books that were written
in Hebrew and had existed for what they considered to be a significant
period of time. Around the same time, however, Greek-speaking Jews were
using an Old Testament canon that included seven other books that were
written in Greek or were of a more recent authorship than those in the
Hebrew canon: Tobit, Judith, Wisdom, Sirach, Baruch, and 1&2Maccabees.
Early Christians used both the Hebrew canon and the Greek canon of the
Old Testament (46 books) as well as 27 books that Christians had come to
embrace as inspired New Testament literature. Early Church councils (in
the 4th and 5th centuries) confirmed these 73 books as canonical meaning
that their authorship was inspired by God. For many centuries, some
continued to question the inclusion of the seven Old Testament books
that were not written in Hebrew. During the Reformation in the sixteenth
century, Protestants established a canon of thirty-nine Old Testament
books, using only those books recognized as canonical by the first
century Jews and dismissing the “apocryphal” books. From this came the
King James version, which remained the standard biblical text in English
until the twentieth century.

Meanwhile, the Catholic Church at the Council of Trent (1545-63) definitively affirmed these seven “apocryphal” books as part of the canon, referring to them as
“deuterocanonical,” which means a “second” canon. Thus, the
deuterocanonical books are those whose Scriptural character, once
contested, have been affirmed as part of the canon of the Bible. No
other books have been or will be added to the canon since we believe
that God has revealed, in and through Jesus Christ, everything that we
need to know in order to find salvation.