When you get that message "This Apple ID has not yet been used in the iTunes store." on your screen, tap Review to sign in, then review your account information.
Click Review repeatedly.
Some people have only had a response after a second or subsequent click.
Try to download a free app at the App Store.
For example try to download this (is an free app).
Log in at appleid.apple.com and make sure you have payment information stored there.
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See also -> Payment methods you can use with your Apple ID
Payment methods you can use with your Apple ID – Apple Support (UK)
fyi: Not all credit & debit cards seem to work with App Store / iTunes Store, try a different one, or preferably a credit card. If your card is not accepted as a paymenf method, you need to contact your bank.