Shinkansen seats are available in four levels depending on the comfort and services your require.
Your seat is reserved and secured when you book your tickets. Head to the station with a peace of mind.
Green Reserved Seat
Better seats and free blankets. Popular among Japanese business persons, executives and people who values comfortable travel. Consider it as "business class" seats.
Know as "First Class" of Shinkansen seats. Only available on Hokuriku and Tohoku Shinkansen lines. Gran Class seats comes with airline-like amenities and meals.The most expensive of all.
You can take any open seats in unreserved cars of any train on the departure date. (No departure time will be indicated on your tickets.) The best seat type if your priority is the cost and are traveling during less-crowded season/time.