Foreign nationals who want to to enter the U.S. should usually get a visa. Visas are divided into 2 general categories:
Immigrant visas are issued to those people who are seeking permanent residence within the U.S., whereas nonimmigrant visas are issued to those people who stay for a limited period of time with a specific purpose.
F-1 visa is usually granted to students for his/her academic degree, for full time courses, valid till the duration of their study period and is not valid for employment. For students planning to extend their stay or to work in US, after the completion of their studies, they need to apply for H-1B visa.
H-1B visa is given out on a lottery system because the demand for H1B visa is more than the supply and it is important to get H-1B visa in order to work in US for students
The H-1B visa is very popular. In order to obtain an H-1B, one must have an offer of employment from a U.S. employer. His/her proposed job position must be in a specialty occupation, which usually means that a bachelor’s degree or higher is required to do the job. The U.S. employer must sponsor the H-1B visa by filing an I-129 Petition
with U.S. Citizenship and Immigration Services (USCIS).
A H2A visa is mainly a visa provision
that allows US citizens to bring nationals from other countries for work in the agricultural fields.
H-2B visa is granted to people who are planning to come to US for a job which is temporary or seasonal in nature. Employer has to produce a certificate approving that for their position there are no employees in US.