Clarification : If you purchase item A (value Rs. 10000, GST rate @ 10%) from reg.dealer. The RD is apply tax Rs. 1000 for above said value.. The govt get Rs. 1000 as Tax for the goods....
If you purchase above item from URD. He ll be billed Rs. 10000 only. The government can't get Tax amount after purchasing URD. So, Govt fall 0... Reason for you purchased from URD. So, You can pay the tax to Govt. That is RCM.....
Working : If you purchase Rs. 100000 from URD. The items tax value is 18%. You pay Tax Rs. 18000. And you can prepare self invoice for your reference also deal it's your ITC for next return......