To understand where your federal income tax money goes, you'd have to read (several times) the 244 pages of the 2014 Budget of the United States Government. Or you could take a look at this chart, which visualizes the budgets for all departments in a uniquely revealing look at our national priorities.
This chart depicts the President's budget request for 2014. The center circle is the discretionary budget: spending that must be approved by Congress every year. It is paid for largely with your federal income taxes and includes all departments within the federal government: a uniquely revealing look at our national priorities (by jess.)