I'm in Tokyo now. I came here from Kyoto by local trains as I wrote yesterday. I used seishun 18 kippu(青春18切符). This is sold at the price of 11,500yen during spring, summer and winter vacation seasons. This is five-ticket set of one day travelcard. You can get on and off the local train all day long, but you can't use an express train or shinkansen. You're allowed to get on local trains. However, if you're in Japan and you don't have much money and you have enough time, it's worth using.
However, I have an advice. Please don't use it under last-minutes travel plan. Because, sometimes trouble may happen and then train may delay...