X will charge GST from Y and pay to govt. And Y will charge GST from Z and thereafter after taking ITC for earlier payment of GST to X, will payremaining amt of tax to govt. For Ex. X sells to Y for Rs 100 and charged GST of Rs 18. Now X will pay Rs 18 to govt. Y will after further processing the material sell to to Z for Rs 200 and charge GST of Rs 36. Now Y will take credit of Rs 18 and paid remaining Rs 18 to govt.