Assuming you're asking what documents you need:
When traveling to Europe from the United States, you will need a passport. Your passport should be valid for at least six months after your planned return date, and it should have blank pages available for stamps. You will also need to get a Schengen visa if you are planning to stay in any of the 26 Schengen countries for more than 90 days. If you are only going to be staying in one country, you may still need a visa depending on that country's requirements. For example, Americans do not need a visa to visit Italy for up to 90 days, but they do need one to visit Norway.
It's a good idea to make copies of your passport identification page and keep them in a separate location from your passport in case it gets lost or stolen while you're abroad. You might also want to consider getting travel insurance before you leave; this can help cover expenses related to lost luggage or medical emergencies while you're away from home. Finally, make sure you have enough money saved up to cover your travel expenses; this includes things like transportation, food, lodging, attractions, and souvenirs