If you have Temporary Protected Status (TPS), you may be able to work while you are in the United States, but you have to ask permission, first. You do this by filing form I-765, Application for Employment Authorization, with United States Citizenship and Immigration Services (USCIS). You should file this completed, signed form when you file Form I-821.
If your requested is granted, you will get what is known as an Employment Authorization Document (EAD). This official document, which is also called a work permit, allows you to work here for a specified period. You can learn more about filing Form I-765 here.