Hi Lewellyn,
Please go through the below URL to understand the basic overview of SAP GTS module .
http://pt.slideshare.net/venkat.gangadi/sap-gts-training-part-2
And also FYI ,, there is no certification exam provided for SAP GTS module BY SAP , Only you have SAP GTS 100 and GTS 200 training programs offered by SAP .
Rama