I want to know what my Apple.com/bill charge is for

Unknown Charge?

1. App Purchase
   1. Curious about a Charge? --> If you see an 'itunes.com/bill' or an unfamiliar charge on your statement
   2. If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
2. Subscriptions
   1. You may view a subscription to an app --> See or cancel your subscriptions - Apple Support
   2. You can also request a refund for a recent renewal of an in-app subscription purchase 

Avoid accidental purchases

1. If it is your device then, please --> Use Guided Access with iPhone, iPad, and iPod touch - Apple ... before handing over a device to a child.
2. If it is your child's device then in the future, enable the Ask to Buy feature --> Request and make purchases with Ask to Buy - Apple Support

It could be Phishing

• Beware of --> Phishing & Other Suspicious Emails 
• Know how to --> Identify legitimate emails from the App Store or iTunes Store 
• Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams —> Use these tips to avoid scams and learn what to do if you think your Apple ID has been compromised.

If you get a suspicious message from your "bank" or from "Apple" about a charge that you don't recognize, don't click on any links in the message to "clear up" the matter. With phishing messages, following such "helpful" links will put you in contact with the crooks who sent the messages, who will use every tactic in the book to scam you.

If you are concerned as to whether the message might be legitimate, look up Apple's contact information so that you know you are speaking with Apple, rather than with criminals.

What Servant of Cats said also applies to your bank. Look up their number on their website (don't click on links in the original message). You can also probably set up online banking so you can just check your account on your own time and not have to wait for customer service to answer the phone - though if there are strange charges you will have to call them.