While the question is short and to the point, in truth its answer is rather complex. Probably the best annotated work which describes the differences between Judaism and Christianity is Rabbi Milton Steinberg's work Basic Judaism, available in paperback.
The essential difference between Jews and Christians is that Christians accept Jesus as messiah and personal savior. Jesus is not part of Jewish theology. Amongst Jews, Jesus is not considered a divine being. Therefore all holidays that have a connection to the life of Jesus are not part of Jewish life and/or practice (Christmas, Easter, Lent, Advent, Palm Sunday, etc.).
Judaism originates as a result of the covenantal relationship between God and Abraham. The Bible (Hebrew Bible which doesn't include New Testament for reasons stated previously) is our sacred literature. The relationship between the Jewish people and God is documented in the text. In the Bible, the history, culture, language, theology, and practices of the Jewish people are presented.
Have additional questions? Visit our Answers to Jewish Questions page.