Boarding a train without reservation being required

That’s how the vast majority of transport across the globe works, you turn up, get on and take an empty seat.

Believe it or not most of the time it works just fine, away from high density city metro systems there is usually enough seating for the demand, and even when not, it would normally only be for a part of a journey with people leaving at intermediate stops vacating seats.

Very much same-same as on the MEL or SYD suburban networks-or those narrow trains that run around Brizzie or even from there to your golden Coast-or like the trams along that coast.

Trains have multiple doors, NOone does checks before and if it is crowded and you want a seat-you may have to walk some coaches-or, more the case lately, firmly ask to remove the luggages from seats (which may also apply to you with the oversized bekpek most seem determined to chug along)

Worth differentiating between trains with optional reservations and those without reservations available. So in Germany and the UK almost all express trains e.g. ICE are optional, but recommended for peak times. They are invariably low cost (0 to 10 euros) and worth every cent.

Obviously for those with no reservation facility it is just turn up and go. These never have limits on how many passengers they will take - simply if they can shut the doors it goes. Normally only an issue at peak hours or when there has been a  previous cancellation.