CQ Press 
How Congress Works [PDF ebook] 

In simple, clear language, the new edition of this classic work presents basic explanations of the procedures and rules that govern the U.S. Senate and House of Representatives. Highlighted sidebars further detail the impact of congressional action with interesting narrative examples from history, along with charts and tables that provide a complete overview of congressional procedures. This edition has been thoroughly updated to reflect the changes on Capitol Hill since 2008.
How Congress Works helps readers place recent events in the context of the entire picture of how Congress operates. A detailed index rounds out this introduction to the real Congress.