In simple langauage , Market research collect the information from the market as per client objective. Then it is analysised insight and put forward to client with the facts and advise. It constitues three key deparments : Research, Field operation and Data analysis. You can choose any of them as per your interest and calibre.
Market research agencies are .. IMRB, ACneilsen, TNS, IPSOS , GFK, and BPO lke WNS, Annik, Toluna etc.