I left Haiti after the earthquake and I have a travel visa for six months. How can I stay in the U.S. longer?
If you have a B2 visa, you can request to extend the time you are permitted to remain in the United States or you can request to change to another immigration status by completing an Application to Extend/Change Nonimmigrant Status (Form I-539). You should speak to an experienced immigration attorney about your options.
Source: USCIS Application to Extend/Change Status
My visa’s valid for five years. Can I apply only for work authorization?
No, the Department of State issues U.S. non-immigrant visas, which allows you to travel to a U.S. border or port of entry and request permission to enter the U.S. It does not guarantee entry and does not indicate how much time you can remain in the U.S. When you entered the U.S., a DHS officer most likely gave you a white card (Form I-94) that told you how long and under what status you can stay in the U.S. If you entered on or before January 12, you should consider applying for TPS. If you entered after January 12th, you can request to extend the time you are permitted to remain in the United States.