when you pin your favourite whatsapp chat it means that whatsapp chat will be seen above all chats in chat list... it will be save... it will be easy for you....
first open your whatsapp and select your favourite whatsapp chat like this
now press and hold it for few seconds to select that chat...
when you select a chat , a new option bar open up at top of window... like this..
press on the option of "PIN" like this
after selecting option "PIN" .that whatsapp chat will be pin and it willl be shown as a sign mark along with chat like this
now your favourite whatsapp chat is mark and it will be shown above all in chat list....
thankyou....