How do I activate the App Store and iTunes?

This Apple Account has not yet been used with the iTunes/App Store -

On a Mac;

• Open the System Settings app (in the  menu)

• Chose your Apple Account

• Choose Payment & Shipping

• Add a payment method to your account details

On an iOS/iPadOS device;

• Open the Settings app

• Chose your Apple Account

• Choose Payment & Shipping

• Add a payment method to your account details

Alternatively -

On a Mac;

• Open the System Settings app (in the  menu)

• Choose your Apple Account

• Choose Media & Purchases

• Choose View Account

• Choose Manage Payments

• Add a payment method to your account details

On an iOS/iPadOS device;

• Open the Settings app

• Choose your Apple Account

• Choose Media & Purchases

• Choose View Account

• Choose Manage Payments

• Add a payment method to your account details

You can find the acceptable payment methods for your country here;

https://support.apple.com/es/HT202631

M1 Mac mini, macOS 15.3.1;  Watch, series 10 GPS-only, watchOS 11.3.1; iPhone 16, iOS 18.3.1; TV 4th Gen, tvOS 18.3; HomePods, audioOS 18.3 and Airport Express w/ Airplay 2