Greetings Attackdog4,
Thanks for visiting the Apple Support Communities! I understand you're curious how you're able to spend an App Store & iTunes Gift Card, as there is a game you'd like to buy and subscription you'd like to renew.
App Store & iTunes Gift Cards are able to be redeemed to your Apple ID balance. The games you wish to purchase need to be available in the App Store for you to be able to purchase them with your Apple ID balance. The following guide outlines how you're able to spend this credit: Redeem App Store & iTunes Gift Cards and content codes - Apple Support
"What you can buy with a gift card
When you redeem an App Store & iTunes Gift Card, you add credit to your Apple ID balance. You can use that credit to make purchases in the App Store, iTunes Store, Apple TV app, or Apple Books. Or you can use the credit to upgrade your iCloud storage or pay for subscriptions like Apple Music, Apple Arcade, Apple TV+, Apple TV channels, or Apple News+.
You can’t use your credit to buy gifts for someone else or buy more gift cards. You also can’t share credit with family members, even if you use Family Sharing."
Kind regards.