For returns

There is Just 1 monthly return GSTR-3

However prior to return one need to file sale annexure details in GSTR-1 by 10th of next month

simillarlly the supplier from whom you purchased  will file his sale annexure which will be available for your confirmation as purchase, any correction , missing entries must be rectified by 15th. this confirmed purchased shall form GSTR 2

finally a return comprising details of GSTR 1 and GSTR 2 shall be prepared which is nothing but GSTR 3- final return with tax liability shall be filled by 20th