H-1B, E-1, E-2, "P", "O", "C", "B": The list of visa types is seemingly endless and just as bewildering as the immigration process, if not more so. These aren't for people wishing to immigrate. There are work visas, tourist visas, and travel visas, and each visa has specific guidelines and requirements. Specific forms also need to be filled out when filing for a visa extension.
The process starts at the US consulate, USCIS or US Department of Labor. An immigration lawyer can help with the details, but these articles will help you understand what each one is for and which is best for your needs.
Find an Immigration attorney in your area.