jr pass

Is the counting of the use of JR pass (7,14,21) begins on the FIRST day is used or when we get to the JR office to validate it?

It begins with the day you specify to be the starting date. You specify the starting date at the time of exchanging the voucher to the actual pass. The starting date can be the day of exchange or a day in the future.

thanks a lot, it solves us a problem. Can you pl tell me, how can we know which train we have to arrange seats and which not?

We are going to spend three weeks all around Japan, so it's a general question, if we can know it now when we plan, before going or we'll have to check each time before going in Japan

The easiest way is for you to tell us where you plan to go and we will tell you.
Usually only long distance trains and some trains from/to airport take reservations for seats. But then long distance trains also have non-reserved seats--first come, first seated. Trains that only go a relatively short distance don't need reservations (they are the type of trains often called commuter trains that stop everywhere). Trains from Kobe to Osaka, Tokyo to Kamakura, for example, don't need -and don't even accept--reservations. Trains from Tokyo to Kyoto, Hiroshima etc. do, but as said above, this is not always necessary.

Thank you