To shanghai someone is to kidnap or trick them into working for you. The traditional way to shanghai someone is to drug him and put him on a ship. When the person wakes up, he better get to work.
This term popped up in the 19th century. The captain of a boat would shanghai people when his ship was short on labor. The shanghaied person would wake up and find himself at sea, often on a long trip like to Shanghai, China. The term is also used for similar, non-naval abductions. If you trick your best friend into coming home with you so she can do your chores, you shanghai her.