The OT actually has very little to do with Christianity. The Old Testament is the Torah, which is very important to Jews. The torah was written by Moses. The Torah contains the basis of Jewish belief. Here is how it influences our religion in several ways:
Moses wrote the Torah, he is more or less the most significant profit in Judaism, next to Abraham.
The torah contains the Mitzvah, otherwise known as Jewish law, which is a collection of 613 commandments.
The torah contains the story of Exodus, which we commemorate on the holiday Passover, celebrating our escape from slavery in Egypt.
Deuteronomy contains the Shema and Kiddish, which our are main prayers, recited in Hebrew
Story of Moses climbing mount Sinai to receive the 10 commandments, seeing G-d with his own eyes.
The Torah is apart of the Tanakh, which is the secret text of Judaism.