Gst on oncarriage

Hello,

I want to know how much GST should be chareged on On carriage.

i.e my company is based in India it is freight forwarding company. i have to do billing for Freight charges from INDIA TO RIGA my client is based out of India so how much gst should i charge him.

As per my understanding the purchase invoice which i will receive will not have any GST in this case how can i charge GST on sale when is it not charged on my purchase

Please help