Analogies with Xian sects aren’t a good idea — they just don’t work because the religions are so different. I would just say, Judaism has always been a religion of laws, the Orthodox believe the law is eternally binding and follow the laws as set forth in the written and oral Torah (while explaining what that is), while non-Orthodox believe it’s not binding (Reform) or that they can change it or disregard it if they don’t like it (Conservative). On the other hand, if you don’t want to say anything negative about other groups (to avoid seeming preachy or judgmental), you could just tell them about what Orthodox Judaism believes and practices.
If you really, really had to make an analogy with Xian sects, it would be something like this:
Reform — Unitarian
Conservative — very liberal Protestant
Modern Orthodox — Traditionalist Catholic
Charedi — More traditionalist Catholics, or maybe Mennonites
There are many problems with this. One is that there are hardly any traditionalist Catholics left; most are “unobservant,” for lack of a better term. Baptists and other conservative Protestants are too hard to match up with any group, because they’re conservative theologically but made a radical break with tradition after the Reformation. I only mention Mennonites (Amish being the most conservative group) because they try to keep out all outside influences and live separately from other people. Unitarian is a fairly good analogy for Reform, because like them they’ve stripped away all the major beliefs associated a traditional religion and replaced it with basic “universal” morality and liberal politics.