You don't! You are not required to understand how ANYthing works. You can be a robot and a slug and let life just happen around you - however, you forfeit any right to complain or get a pass on the argument of ignorance. This works whether you get us in deeper hot water by electing some slick talker or screw up your car by not changing the oil or get shafted by the plumber because you don't know what flows downhill.
I think it's important for all citizens of the United States to know how their government works (or doesn't, as the case may be). There may be something that you are passionate about getting changed in this country, and the way to go about it may be to get a bill put through Congress. By knowing what all it entails, you'll know how to go about it.
People who don't understand how our government works fill the ranks of the Tea Party and other groups that advocate for ridiculous ideas. I've seen too many people trying to answer questions on this site that have no idea what they're talking about. If you don't care about your government, then by all means don't vote, we don't need ignorant people making decisions about how we live.