The Christian Bible has an Old Testament and a New Testament: the NT was produced by the Apostles or with apostolic approval. The OT is the Hebrew Bible.
As I said before, the Protestant OT is essentially the same as the Hebrew Bible (which the Jews call the Tanakh).
The Roman Catholic OT differs in that it has kept sections which originated from the Septuagint version. For example, you could look at the RC Jerusalem Bible online at https://bibletold.com/esther/ and compare Esther 8:12 in this version with the King James and the Jewish JPS version at biblehub.com: the Jerusalem version has an extra 21 verses at 8:12. Compare also Esther 4:17 and chapter 10. In addition to differences within books the RC OT has extra books not found in the Tanakh or the Protestant OT.
The Septuagint was a Greek translation of the Hebrew OT produced before the birth of Christ for those Jews who could no longer read the Hebrew. (When the OT is quoted in the New Testament the reading is often taken from the Septuagint. This, we believe, was not an emphatic endorsement of the Septuagint... it does show, though, that it was not altogether bad, and it shows that a proper understanding of the intention of the text is more important than accuracy of the text.)
When in the second century Jews began to see differences between the Septuagint and the Hebrew versons they abandoned the Septuagint readings.
At the time of the Reformation the Protestant reformers abandoned the Septuagint derived texts in favour of the Hebrew Masoretic text, though in a few small cases they retained the Septuagint reading (- such as in Psalm 22:16 "they have pierced my hands and my feet" rather than the Masoretic "like a lion are my hands and my feet": the Dead Sea Scrolls reading vindicates the reformers choice of the Septuagint reading in this case.)
What is really important to understand is that the Jews tend to see the moral commandments of their Tanakh encapsulated in the 10 commandments in a different light to Protestants. Judaism would tend to see these commandments as something it is possible to please God by obeying perfectly. Evangelical Protestants maintain that it is impossible to keep them perfectly and that they were designed to show us our failure and need of a Saviour. The Protestant understanding is that the 10 commandments must be kept 1 Out of love to God; 2 zealously; 3 from the heart; 4 in order to bring glory to God; 5 Because God commands them; 6 that where commandment forbids (eg thou shalt not bear false witness, thou shalt not kill) the opposite positive virtue is to be understood as also commanded; 7. Each commandment is to be understood as forbidding the worst example sin and as representing a whole family of sins (eg thou shalt not commit adultery includes all the family of sins of sexual impurity such as lust of the eyes, immodest dressing, etc). (An example work having this teaching would be "The Marrow of Modern Divinity" by E. Fisher, but you can find it everywhere).
According to the evangelical understanding, if we fail to always keep the 10 commandments always out of love to God, zealously, etc, then we have failed and need a Saviour... the 10 commandments were designed to show we need a Saviour. Once we trust Jesus as our Saviour then we try to keep the commandments not in order to try to win God's favour but because we already have it and want to try to please Him.
Jews today, if they are religious at all, and many are not, have a Judaism in which it is up to them to try to gain God's favour by their own obedience. For Protestants salvation comes by trusting in the shed blood and in the perfect obedience of the Lord Jesus Christ, and by a repentance resulting from confident faith in God's mercy offered through Christ alone.
[As an aside, praise God, many Jews today are Christian, with about 1.6 million in the USA alone -https://en.wikipedia.org/wiki/List_of_converts_to_Christianity_from_Judaism]