This is, of course, an incredibly subjective and contested question. For millions of people, notably Christians and Jews, the Old Testament is the divinely-inspired story of the Jews in history and God's plan for humanity. Even for Muslims, some of the Old Testament patriarchs, such as Abraham, are important figures. Many conservative-republican Americans looks back to the Old Testament, namely the Ten Commandments, which you can find statues of around the country, as a source for our country's laws and morality. Many cite the founding fathers as faithful Christians who were creating a Christian nation, even though many were Deists.
As far as the Old Testament as a source for truth, that's an impossible question. If you believe in it, then sure. But if you're a skeptic, it's far more complicated and problematic." And while there seem to be self-evident truths in the Old Testament, such as you shouldn't kill other people or sleep with your neighbor's wife, there are also confusing moral pronouncements on violence, women, other cultures, and how to be good.
The composition of the Old Testament is also complicated, as it was written over a long period of time by various writers and in a number of languages. Although, again, those who believe in it would say that the writers don't matter because God was inspiring their writing. I'm not sure it's a question that the professional educators of eNotes are equipped to answer. Consider consulting a rabbi or priest.