What are apocryphal books?
Apocryphal books are books that are not part of the official Bible list. Apocryphal books may have historical and moral value but they were not inspired by God, so they are not used to form doctrines (fundamental teachings). The Catholic Church and the Orthodox Church accept some apocryphal books as part of the Bible.

"Apocryphal" comes from a Greek word meaning "hidden". The Bible has 66 books that all churches accept as inspired by God. Several other related but uninspired books have also been written over time. These books are called apocryphal books, because they are not part of the Bible (they were “hidden” from the Bible, to avoid heresy and confusion).

See more about the books of the Bible here.

Apocryphal books may have interesting and useful information, but they also have dubious teachings, which contradict the rest of the Bible. Some have fanciful stories and historical errors. His teachings do not have the same value as the word of God (2 Peter 1:16). Therefore, they are not published together with the Bible. It is not good to mix truth with error.

What apocryphal books are accepted by the Catholic Church?
The list of apocryphal books accepted by the Catholic Church is:

Tobias
Judite
The Wisdom of Solomon
Churchman
Baruch (and the Letter of Jeremiah)
1 and 2 Maccabees
Excerpts added to Esther
Excerpts added to Daniel

These books are called "Deuterocanonicals" in the Catholic Church, because they were only officially accepted as divinely inspired in AD 1546. All of these apocryphal books belong to the Old Testament and are not accepted by Jews as being inspired by God.

In addition to these books, the Orthodox Church normally accepts:

1 and 2 Ezra
The Manasseh Prayer
3 and 4 Maccabees
Psalm 151
How were the official books of the Bible chosen?
In the fourth century there were many books in circulation in the churches, but not all were authentic. To avoid heresies and contradictory teachings, the early church decided to do a great deal of research to decide which ones were authentic (1 Thessalonians 5:21).

Church leaders and Christian scholars came together in councils and investigated each book. Only books with solid evidence of authenticity were included in the Bible, leaving out any books that left doubts.

See also: who wrote the Bible?

The apocryphal books accepted by the Catholic Church and the Orthodox Church were not accepted as divinely inspired by these councils, but were popular books, considered useful. They were a bit like the books that many Christians write today - enlightening, but they don't have the same authority as the Bible.