See the red print on the bottom of the card that says "Do not share your code"? The Gift Card is for you to redeem in the App Store on your device, not to be traded for any other service or goods. Once someone else enters your code into their account, you have lost your money.
After you redeem the code on your device, this is what it can be used for:
What you can buy with your Apple Gift Card or Apple Account balance - Apple Support
If you have problems redeeming your Gift Card, then you can review the information provided here.
If you can't redeem your Apple Gift Card, App Store Card, or App Store & iTunes Gift Card - Apple Support
You might also want to make yourself aware of the common Gift Card scams:
About gift card scams - Apple Support