To legally work in the United States, you must be sponsored by a U.S. employer for the appropriate working visa. There are several categories of working visas. The visa you will hold depends on your background, experience, nationality and your proposed job duties.
The visa application process is initiated and driven by your U.S. employer and is not something an individual foreigner can do on his or her own.
There are two basic types of working visas. Non-immigrant visas allow you to live and work in the U.S. for a defined purpose for a defined length of time. Immigrant visas, also known as green cards, legally authorize a foreigner to permanently live and work in the U.S. Because green cards take a long time to obtain, most foreigners will initially enter the U.S. to work in a non-immigrant visa category.
Your employer will work with immigration counsel to identify the appropriate visa category for you. The employer will file a visa petition requesting your visa from the U.S. Citizenship and Immigration Services (formerly the U.S. Immigration and Naturalization Service).
If you are already in the U.S. via another visa category when your employer files the visa petition, the employer will request that your status be changed to the requested visa category. If you are overseas when the employer files the visa petition, the U.S. Citizenship and Immigration Services will send petition approval via your local U.S. consulate. You will apply for your visa there; and then you will be able to legally enter the U.S. and begin work.