WHERE CAN I ACTIVETE THE JR PASS

Hello!
I will arrive to Japan through the Chitose Airport in Hokkaido on Nov 29th, but I will not need the JR Pass until Dec 4th to travel from Sapporo Station to Tokyo st using the shinkansen, as much as possilble.
My questions:
1. Where can I activate the JR Pass.
2. Where have I to cath the shinkassen in Hokkaido?

Thank you in advance for your comments.

Best regards.

Ladanca