Apply for a passport as soon as possible.
Some countries also require U.S. citizens to obtain visas before entering.
Check with the embassy of the foreign country that you are planning to visit to see if you need a visa. Make a copy of your passport's data page. Make a copy of your passport's data page and any visas. Keep it with you, but separate from the originals, at all times while traveling. Remember to leave an itinerary with family or friends.