Yeah sure can use it inside a country. 

Keep in mind that only 2 travel days can be used in your country of residence.

To travel with the pass using an included train, you always need to use a travel day.

I’m not sure I understand the question.

As soon as you activate a trip, then you are using a travel day, and you can continue to travel that day.

Or of course you can travel outside of your pass (eg buying tickets somewhere else, or car/ train/ bus).