Where can I learn about how the US system of government works?

I get a bit lost sometimes there are branches and offices and position and so forth. I would like to have an overall grid understanding but also a more specific one. And if I am leaving anything out like how people are elected, the electoral college, and so forth. That just seems a bit complex with caucuses "whatever that is" and such. I am looking for sites, videos, books, or if you want to sum it up...