You should always register your journey in the app. If no reservations are required, then that is all you need to do. Also see this page under "Getting ready to board the train”.
EXCept it seems in LT=LIetuva=Lthuania for you: there one always has to find/go to counter to get a ticket for 0.
In ESpana-on cercanias/rodalies and in FR/Transilien around Paris-there are gates anywhere-you have to ask at counter for free passage ticket or let them open it remote.
There are also many gates in Nl and GB-pass by using code or by the manned desk.