On these trains you simply board the train and find a seat.
Reservations are optional but not required for these trains:
ICE(Intercity-Express, the most common high-speed train)
You can always hop on the ICE but if you want to be sure of a seat, you should make a reservation. This is especially recommended during rush hous, during public holidays and in the busy high season.
Fees: 2nd class: € 4.50 / 1st class: € 5.90
EuroCity and InterCity (domestic trains)
Fees: from € 3.50