Help me please!!

I’ve had this app for a couole weeks now, but there are a couple things that I'm confused about. If anyone can help me, please do.:) So, I have an apple and I still want to use the Google Play giftcard. Is it possible that I could still use it? And, I was wondering if you could buy multiple of the same giftcards and make giftcards with more money on them. If anyone can help me, if you're able to respond to this ( I've never posted one of these before) please tell me. <3 Have a blessed day.