Can u please explain more for me abt the index & match here??

=IF(AND(INDEX(Sheet1!$D:$D, MATCH('Sheet1 (2)'!$A3, Sheet1!$A:$A, 0))=Sheet1!$G$4,INDEX(Sheet1!$C:$C, MATCH('Sheet1 (2)'!$A3, Sheet1!$A:$A, 0))<Sheet1!$H$4), Sheet1!$J$4, $B3)