The H-1B visa allows a limited number of skilled and certain unskilled employees to work in the United States. It is based on a petition filed by an American employer. The most common careers of H-1B visa holders are nurses, math teachers, and computer science professionals.
Paid work is generally not allowed on a B1/B2 visitor visa. Working unlawfully in the United States runs the very real risk of arrest, deportation, and ineligibility to re-enter the US. Illegal immigrants also run the risk of dangerous work conditions.
If you are seeking to adjust visa status or to enter the US on a working visa you should first check the official government websites of the US Department of State, which issues visas abroad, and the U.S. Citizenship and Immigration Services which administers immigration programs within the United States. Unfortunately, con artists both in the US and overseas often prey on people's desire to travel or work in the US. Keep in mind that US visa applications do not usually require an attorney or other intermediary; be wary of and verify any "advice" offered by third parties.