Hi! So I’m planning my trip that I am about to do during late autumn/winter and I really want to make it as a cheap experience as possible. Therefore I am aiming for trains that doesn't require reservations

I am totally new to this but I have done a lot of research, though there are some formulations I can't wrap my head around. For instance when I search for connections with no reservation required I sometimes see this grey statement that there is no information available about that particular train, even thought I only chose to see search results with no reservations. What does this mean? Is it cancelled or is it a commuter train with no booking what so ever?

Also when I look up connections on the rail planner app it doesn't necessarily say this, it just says when reservation is mandatory, but when I check the facilities it sometimes says “no reservation on part of journey”. Does this mean that there is a specific distance during that ride that costs money? It often says this when a regional train with no mandatory reservation crosses a boarder between countries, France and Italy for ex.

This might be a very confused text haha but I really don't want to pay more than necessary but I also don't want to be thrown off the train… What does all this mean?