H-1B, a non-immigrant visa in the United State, allows U.S. employers temporarily to employ foreign nationals in specialty occupations. Questions about this visa are quite likely to be Closed as outside our scope though they may belong on Expatriates: http://expatriates.stackexchange.com/tour.
Individuals cannot apply for an H1B visa to allow them to work in the US. The employer must petition for entry of the employee. H1B visas are subject to annual numerical limits.
US employers can begin applying for the H-1B visa six months before the actual start date of the visa. The typical duration of the visa is three years and is extendable to six years.