Judaism is a monotheistic religion practiced by the ancient Israelites, whose descendants practice it today. Judaism is over 5000 years old, and may be the first ever monotheistic religion in the world. Judaism is based off the teachings and laws of the Tanach, which is split up into three sections, the Torah (literally "Teaching) The Nevi'im ("Prophets) and the Ketuvim (writings).
There are many different sects of Judaism, there are Liberal Jews and there are Conservative Jews. One good point about Judaism is that Jews think they shoud make the most of the good things in life, good things are seen as a gifts from God and making oneself unhappy through self denial is not part of Judaism.