How to Get a JR pass
You purchase a
Exchange Coupon prior to arriving in Japan, I use
JTB Travel but there are a other sites offereing them.Allow two weeks for it to be delivered.
You cannot purchase a JR Pass in Japan.
Once you arrive in Japan you go to the Shinkansen Ticket Office in the city you are staying (assume landing in Tokyo or Osaka) and exchange you a
Exchange Coupon for a JR Pass
You can specify the dates you want to activate it .
If you have a few passes for a few different dates , exchange them all and set the dates at that time