The main sects of Judaism in the United States today are Orthodox, Reform and Conservative, according Judaism 101. About 5 million people practice Judaism in the U.S.
The Orthodox sect is the most conservative of the three. Practitioners believe that the Torah came directly from G-d, how Jewish people spell "God," to Moses, and that it is something that should be followed strictly.
Reform Judaism is the most liberal. Believes in this sect do not think the Torah was written by G-d and do not follow its tenets strictly, although they do keep the spirit of Judaism.
Conservative Judaism is somewhere in the middle. The believe Torah was given by God, but that it came through human beings.