Explain this entry please

Dear student 
At the time of purchase of goods INPUT CGST and INPUT SGST is paid by the person who is purchasing these goods 
In the above entry 6% CGST & SGST is paid by the purchaser on the purchase of goods of Rs. 40,000 by him 
CGST = $40,000\times \frac{6}{100}= Rs. 2,400$
SGST = $40,000\times \frac{6}{100}= Rs. 2,400$
TOTAL AMOUNT PAYABLE AT THE TIME OF PURCHASE = 40,000+2,400+2,400 = 44,800
AMOUNT PAID BY CHEQUE                                                                                       = (20,000)
AMOUNT DUE TO BE PAID AFTER 2 MONTHS                                                         = 24,800
Regards