-Through real letters/conversation
-Play wherever you want, in a lake, a ship, a home, a box, as long as you are writing letters to a partner / conversing with a partner as if you were its fine.
-Anywhere, as long as the partner is human. Try reddit.
-When it reaches it's natural narrative conclusion, when does a film end? when does a book end? When it's reached an appropriate narrative finale, or maybe never, if you prefer.
This is a TTRPG (tabletop role-playing game), you play through real correspondance. As for if it is really left without enough info, the rules were really written for someone familiar with such games already, so its more just not enough for you, not its target audience (not to say you shouldn't play).
It is also in the "physical games section" on the store, so its not abnormal to be downloadable rules/books not a program. But its understandable that this is confusing to you.
A program is merely one way of experiencing a story or game, equally it can be done through a board, through conversation, through letters, or even through reading something on your own.