Someone made a purchase in another country with my Apple ID, what can I do?

Check to see if there really was a purchase by looking at your purchased items list in iTunes.

Thousands of such fake messages go out every day. The idea is to get you to click on a (usually, VERY big button) to cancel the payment, login to your account, or similar. From there, you're taken to a fake site that looks like Apple's. What they want is your Apple ID and password. Others go further and ask for things Apple never would. Like your Social Security number, mother's maiden name, etc.

Real messages or emails from Apple do not include any such links. They do not have attachments of any kind. They are very careful about proper spelling and grammar. Fake messages are usually loaded with poor English.