United Nation - Trade Statistics Database (comtarde)

These are a very useful website to understand trade classifcation also to obtain foreign trade data online

http://comtrade.un.org/

Comtrade database
http://comtrade.un.org/db/default.aspx

Comtrade Manuals and Documentations on how to extract data from comtrade databse
http://comtrade.un.org/kb/article.aspx?id=10104

List of Trade Classification such as SITC, BEC, ISC

http://unstats.un.org/unsd/cr/registry/regct.asp?Lg=1

Details of SITC classification

http://unstats.un.org/unsd/cr/registry/regcst.asp?Cl=28