There are several possible means by which you can become a lawful permanent resident. A lawful permanent resident may work in the U.S. without any restrictions.
There are other means by which you can acquire a non-immigrant visa. Some allow you to work in the U.S.; others prohibit employment. Because this is a complex issue depending on each personal situation, you should seek legal counsel with an immigration attorney.
US Citizenship & Immigration Services
U.S. Department of State
Please contact us with any questions about your particular situation.