How to make compound g
can somebody give a detailed explanation?

I'm slightly confused by your question as it tells you that G is produced by reacting E with aqueous bromine, but the structure of G is not shown so I am assuming that you would like to know its structure. In this situation a number of additions could occur, but I believe the most likely is addition of the bromine across the C-C double bond, resulting in a dibromo structure where each bromine atom is bonded to an adjacent carbon.