I need to know what this charge is for?

If you're sure that that message comes from Apple AND if you've already checked your bank statement reporting that amount, see this support article:--> If you see 'apple.com/bill' or an unfamiliar charge on your statement - Apple Support

Regards

Giulio

To add to what Giulio has stated, if you received an email, it is possible that it is a phishing attempt to gain your account info. See this, Identify legitimate emails from the App Store or iTunes Store - Apple Support

However, if it showed up on your bank statement, then the link Giulio provided is your best bet.