why is apple charging me if i didn’t buy anything

If you didn’t buy anything the won’t charge you. You might want to check if you have a subscription to something from an app or anything of the like. You can check this by going in your settings. Goto Settings > Click your AppleID at the top > Subscriptions.

All of your subscriptions will be located in here and the date that they will be charged. If you don’t want to keep that subscription active, you can cancel the subscription from there.

This is a user to user forum and Apple is not here. We have no way of seeing what you are seeing. See if this helps: Subscriptions and Billing - Official Apple Support

When I saw a charge from Apple, I wondered too. Then I realized I had upgraded my iCloud storage. Another charge was when I subscribed to Apple + TV.

Hello ~ Where are you seeing this charge?

~Katana-San~

If you're being asked to add a payment method to your account when attempting to download a 'free' app, that's because you MUST have a payment method registered to download apps that support in app purchases.