Question about reserving seats on Shinkansen

Greetings,

My wife and I will be arriving in Japan April 29th and staying for two weeks, leaving on May 14th. We plan to travel to Kyoto on May 3rd and I was advised by a friend that we should reserve seats for our shinkansen tickets as during Golden Week the trains will be extremely busy.

However, I am not sure how to go about doing that with my JR pass. Any advice would be appreciated. Thank you