You do not apply a pass to a seat reservation. A pass entitles you to travel. Seat reservations are optional and always extra, regardless of where your travel entitlement comes from. And they always come at a cost. You do not even need to be in posession of a ticket to make a reservation, but of course must have a ticket once you are on the train.
Local trains never have reservations. You an always board a train, there is no uncertainty to eliminate. Just be at the platform on time (ie. a minute or two before departure). Get on. Find yourself a seat. Usually there are plenty of seats. Occasionally more people board a train then there are seats, and then some people stand till the next station, where there are almost always some people getting off, freeing seats.
Trains are mass transit. Think of them as a subway, but with nicer trains and scenery.