Can I use my Apple TV in Europe?

You might be more specific about which Country in Europe: Apple TV will worked in most, but not in all and some countries might have limited or no access to some content.

Go to Apple's main page related to Apple TV and check what content will be available in the country to which you are going.

If you have a US account accessing US content then yes you "should" be able to take it over seas. You will need an internet connection where ever you are. If you are asking as a citizen of that area can you use it then yes, but iTunes the country you have an account for might have less content available. Also many of the apps and add-on features may not work for non-US accounts.