Query for GST rate

hello,

my bussiness is online form fillup for compititives examination as like IIT/PMT/UPSC/SSC etc.

for exmple-
My form official rate is 1000/- and i take 1100/- from custmer. then how i can calculate GST rate?

i want to know about gst charge, 1st is GST Charge aplicable for all 1100/- and 2nd is Gst charge aplicable on 100/-.

one more ques. is Gst charge(%) aaplicable for both condition. what is right for Gst rate 1st or 2nd??

please reply as soon as possible.