If you travel on a Eurail Global Pass, a Eurail Select Pass, a Eurail Regional Pass or a Eurail One Country Pass, you can only use a free benefit on a day which you fill in on your Pass (a travel day). For free passage on international routes, the Eurail Pass must be valid for the country of departure AND the country of arrival. For domestic travel, your Eurail Pass must be valid in the country you travel in.
Please note that reduction benefits do not require the use of a travel day on your Eurail Pass. If traveling at a reduced rate, the travel may take place at any time, provided it is within the overall validity of the Eurail Pass, even if all the travel days in the calendar have been used up. For a reduced passage on international routes, the Eurail Pass must be valid for the country of departure OR the country of arrival. For domestic travel, your Eurail Pass must be valid in the country you travel in.
Some trains may require passengers to have a seat reservation
Seat reservations may be compulsory or highly recommended on select European trains. The cost for a reservation or supplement is not included in a Eurail Pass and varies depending on the country, type of train and date of purchase/travel. High speed trains and night trains are examples of trains requiring a supplement and reservation.