what is the process of declaring money more then 20K RMB

I am from India and want to take 25kRMB cash in China,I know more than 20k rmb need to declare in customs but this is my first time so I would like to know the process of declaring of extra money-
I need to declare in India or after reaching china ?
Do I need to pay any extra amount as a fee?
on the airport where I need to tell that I have extra money ?
is there any special document I need to carry with me for declaration?