Typically when people think of laws they think of statutes: written laws enacted by legislatures

Because of federalism,  more than one legislature enacts laws in the United States. Congress passes national laws and also each state passes state laws. 

Federal statutes are codified in the United States Code.  Similarly, each state codifies its own statutes.

Statutes and the Constitution

As a general rule, state statutes apply to anyone who lives within a state while federal statutes will apply nationally, to everyone living in the United States.

But keep in mind that the Supremacy Clause establishes the Constitution as the supreme law of the United States,  As a result, if there is a conflict between a statute and the Constitution, a court can nullify the statute by declaring it unconstitutional.

Stages of Passing a Bill

How a Bill becomes a Law

Step 1: Introduce the Bill

A member of the Senate or the House of Representatives will introduce a draft version of the Bill.

Step 2: Committee Review

A committee will review the draft bill and edit it.

Step 3: Floor Debate

Depending on whether the bill was first introduced in the Senate or the House, that chamber will debate and vote on the bill.  If the bill fails, then the bill will die.  If that chamber passes the bill (e.g., House of Representatives) the other chamber (e.g., Senate) will then review, edit, and vote on the proposed law.

Step 4: Reconciling the Act

Once the bill passes one chamber of Congress it is known as an Act.  The other chamber must also vote on the Act.  But it is possible that the other chamber will modify the Act.  This creates an issue because the Senate and the House of Representatives cannot send different versions of the Act to the President.  Instead, a committee from both chambers of Congress will edit the Act so both chambers can vote on the same version.

Step 5: Sending the Act to the President

If Congress passes the same version, the Act will be sent to the President.  If the President signs the Act it will become a law.  The President might veto the law, in which case Congress can override the veto by a 2/3 majority of both houses.