I'm going to be taking some Regionale trains on day-trips. Is it still a situation where you buy your ticket, stamp it in the machine, and just jump on any (Regonale) train going to your destination? Or do you have to commit to the times for the whole journey? If there's a change of trains and I want to spent a hour or two in that town before continuing my journey, do I need to buy a ticket to transfer town and then a ticket from transfer town to destination? Or just jump off and then jump back on when I'm ready to continue?

Paper tickets needed to be stamped and aren't tied to a train or seat. If you use the app it's tied to the train and the next four hours.

https://www.trenitalia.com/it/inform...renitalia.html

Yes you can't hop on and off. You need to buy tickets point to point.