Congress.gov is the official website for US federal legislative information. The site provides access to accurate, timely, and complete legislative information for Members of Congress, legislative agencies, and the public. (Image Source)
Each senator have their own website which can be reached by their lastname.senate.gov. These sites contain important statements and press releases about current senate activity.
The US Government Publishing Office (GPO) is the Federal Government's official, digital, secure resource for producing, procuring, cataloging, indexing, authenticating, disseminating, and preserving the official information products of the US Government. The Catalog of Government Publications is the finding tool for these publications. (Image Source)
There are many different types of Government documents that are related to the Congress and the Presidency. In order to find information efficiently, take a moment to think about the kind of information you are trying to locate:
Check out this "Key to Legislative Citations" table on the U.S. Senate website for explanation of what each part of the citation signifies.