Taxes in the United States are one of those topics that everyone seems to know about, yet be fully ignorant on the matter. On the one hand, we all pay taxes so we know about them. On the other hand, the various complexities of the system make them very obscure.
And when the politicians get their hands on the subject their goal is to further muddle the waters rather than make them clearer.
This is video from Vox is a great way to explain how marginal taxes work. So in the future you will be better prepared to deal with the subject.