How to use TAJ gift card/Taj experiences gift card?

Hey folks, has anyone use Taj gift cards for Booking?
can anyone please explain me, how does it work?

From what I read from the term and conditions it cannot be used online.
It can be only used  only offline.
if that's true, how does it work?. 
Can we use it on top of the member rate?
or vouchers are valid only on base rate?

if anyone can please share their experiences of redemption that would be great help
Also do the gift cards work differently from different sources like gyftr, wohooo, Amex?
or all Are the same?