Hi Vudanrao,
As you told that you are already into SAP SD Module, hence it will not be difficult for you to learn and practice SAP GTS module as it much derived from the R/3 Foreign Trade itself.
Also, there are a couple of good books already in the market to assist you on the complex and new topics included in the SAP GTS Module, which you can reference. In addition, you should also keep involved in the ongoing discussions at the GTS SCN forum for new learning from experts.
Still, if you feel like being confused on any topic, please post your questions here for experts. I am sure, experts will make you understand the topic in a better way.
Regards,
Aman