A ticket is for a route. It permits you to take trains on the route you bought the ticket for. For train travel you always need a ticket.
A reservation reserves a seat for you on a particular train. That guarantees that you will have a seat on that train. Without a reservation you can still take whatever train you want (provided you have a valid ticket) and just look for a free seat on the train.
Few people actually bother with reservations here. You do need a ticket though.
