Just quickly, off the top of my head: Generally, Conservative Jews keep kashrut -- but, unlike Orthodox Jews ordain women, and have other liberal positions. Reform Jews generally reject the need to keep kashrut, take more of the Torah symbolically or metaphorically. An outward example: in the synagogue I was involved in, Conservative Jews tended to wear the kippah (skull cap/yarmulke) all the time, and maybe the fringed garment (tzitzit); Reform Jews donned the yarmulke only during services, and didn't wear the tzitzit at all. They used different prayer books (siddurim). Theologically, there might not be many real differences -- although Reform Jews (like some neo-Hasidim) seemed to tend more toward some versions of pantheism. Humanistic Jews might reject the notion of a supernatural creator God (or any God) altogether, but still keep some of the Torah-traditions as a community-bonding practice.
That is really simplistic, but the best I can do to give maybe a picture. Wikipedia probably has articles, but these observations are based on my personal experience.