On the national level, this can be found at http://votesmart.org/education/government. It includes, for example, the parts of government, and how a bill becomes law.
We have completed a more in-depth course, complete with 13 interactive quizzes. We suggest you start with a quiz, and if you don’t do well, you then read the related course chapter. Our politics 101 course is here, and the quizzes for the course are here.