Need help with {vouchers x rewardpoints} using infinia

I have an infinia cc. Planning to get a mobile worth 1,10,000 and options are Flipkart,chroma and reliance digital.

I was looking at the vouchers and couldn't really get my head around it. Can someone please help understand how gift vouchers work or how I could use it and any hacks to get a good deal? TIA :)

( I know it's a very basic question. Started using credit card very recently, so apologies for my lack of knowledge)