Congress passes statutes that then become law.
Once a statute becomes law, it will appear in different forms over time, which affects how you are able to find, read, and engage with the content.
You can find slip laws listed on the Public Laws page of Congress's official website.
New statutes will appear within days of becoming law, so this is a good resource for finding brand new statutes.
Session laws are available through the United States Statutes at Large.
This is intended to be a more permanent home for federal statutes but is only compiled at the end of a congressional session. The Statutes at Large can be useful for finding legislation published around the same time or during a particular administration.
The United States Code (U.S.C.) is freely available online through multiple sources.
You'll find it organized by topic (titles) with individual chapters and sections that provide the full text of the legislation. When it comes time to cite a federal statute, it is best to cite the U.S.C. since it is the official version of the code.
The United States Code Annotated (U.S.C.A.) is available to us through Westlaw.
Even though this is an unofficial version of the United States Code, the U.S.C.A is the best place to begin researching statutes that relate to your topic. The annotations will point you to valuable resources that will give you a more complete understanding of how a statute has been cited, challenged, and interpreted.