Hi Aisha,
welcome to the Apple (user-to-user) Community!
Re: "Account Review"
Your Apple ID is the account you use to access Apple services like the App Store, Apple Music, iCloud, iMessage, FaceTime, and more. It includes the email address and password you use to sign in as well as the contact, payment, and security details you use across Apple services.
If you wish, you can log-in to your account online anytime, and to check everything is up-to-date:
Apple ID Log-in
https://appleid.apple.com
If needed: How to: Get a verification code and sign in with two-factor authentication - Apple Support
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Re: "a message 'you need to review your account' keeps popping up,
preventing me from downloading any apps etc."
What to do: If you can’t download or update apps on your iPhone or iPad - Apple Support
or
If your payment method is declined in the App Store or iTunes Store - Apple Support
If needed: (info. / support / contact)
Apple ID support website Apple ID - Official Apple Support
or
App Store support website : App Store - Official Apple Support
All the best :-)