You might be interested in some older threads on this topic:
What factors went into play when deciding which books would be included as biblical canon?
Why were there so many Gospels written some of which were accepted in the canon?
Why are the books of Enoch not included in the Bible?
When and why was the Gospel of Thomas excluded from the Biblical canon?
Why did Early Christians remove the book of Maccabees from the Bible?
There's different criteria depending on which part of the Bible you're talking about (the Old or New Testament). For the Old Testament, much of it was based on the Jewish canon, but with a few exceptions that I think really highlight some of the disagreements among church founders. For instance, some books were included in the Christian Old Testament because they had been included in the Septuagint, while other church founders felt that that didn't matter, and that it was the original Hebrew Bible that mattered. The former section includes things like Maccabees and Ben Sira, which are included in Catholic and Orthodox Bibles, but not Protestant ones.
With the New Testament, there is a gradual assemblage of the canon, but also agreement on it within a few hundred years. Here, canonicity was determined partly by whether or not there was a belief that the work was written by the person it was claiming to be written by. The Pauline Epistles, for instance, were pretty clearly written by Paul, and Paul had clearly been divinely inspired, so those were allowed in very rapidly. Works like the Epistles of James and Jude, though, were more heavily questioned in their authorship, and so weren't allowed in. The books also had to agree with the accepted theology of the church. This meant that Gnostic texts like the Gospel of Thomas, while read, were not acceptable because their image of Jesus did not match what had come to be understood as Jesus.