Every country has their laws & regulation to maintain democracy & peace in the country, similar ways in US there are Federal laws. Federal laws are applicable to all US & non US citizens staying in US. We can say that anyone who enters in US till the time he/she is us will governed by US federal laws.
There are some subjects govern by center authority in a county hence federal laws help them to manage & control on activities such as : Immigration from other countries, Social Security act & SSI social security income act, Civil rights , Patent ,Criminal laws ,Bankruptcy.
Major domestic laws are governed under state level. In US there are 50 state there are control for Family teasing matters, Divorce, inheritances, property matters handled Business at state level govern by state laws so business contract are designed as per state law .
Some accident cases or medical malpractice or injuries at work also come under state governed.
To create Federal law there are steps which are followed A) Produces proposals to national committee B) Create bill & national council take it to the committees for discussion. C) Next step it goes for federal council for legislative procedure check & veto. D) Once it gets full veto before it force in public need authentication by signature of president. E) Once it’s authenticate it gets published in the Gazette.
All above mentioned procedure take place in parliament, so to the public parliament discussion starts from step A to E.