Most high speed trains between major cities, such as TGV trains in France, require seat reservations. These reservations usually cost three or four dollars. You can make reservations easily at any station or at local travel agencies in Europe. One day in advance is normally plenty of time. If you're not sure, ask at a ticket window, or on the platform before boarding.
Most night trains offer a few different sleeping options.
You can usually sit in a regular seat all night for no reservation fee, but this can be uncomfortable. We recommend reserving a couchette. Couchettes are bunks, with pillows and blankets provided. They're a fun way to meet other travelers. Compartments with fewer people are sometimes available, but prices increase as the number of people decreases.