US visa categories are divided into two types: non-immigrant and immigrant. Non-immigrant visas are temporary and allow a person to enter the US for a particular activity in the US for a limited period of time. Immigrant visas are permanent visas, otherwise known as a “green card” and allow a person to reside permanently in the US.
In general, to obtain a US work, a person must have an offer of employment from a US employer or a foreign employer must transfer an employee to the US. If a person does not have a US offer of employment, there may be limited visa options available.