papers, like a basics why a company wants to hire you vs Americans. This is, probably "sponsorship" if it is not sponsorship for "green card". You use it to get TN (or new termin for this) permission on US border (it takes 30 min) then you go to US, apply for SSN and start to work. Last I know TN work permission was on 3 years. This is all depends from US employer, offer and support papers. In my case it was a recruting company and I was an employee there but worked in Samsung. I was an employeee, but with a condition that it depends from Samsung ability to extend contract every 6 months. I've been worked there for 4 years and left when I've got an offer from other company that was agree (verbally) to sponsorship my Green Card.