Instead, just show your pass to the staff in the glass booth next to the gates. They will let you through the gate in front of it.
Once inside the station it is quite easy to find a platform as they are all numbered and the indications concerning the lines and directions are everywhere.If, however, it is not clear, don't hesitate to ask the other travelers who, in most cases, will be happy to help you.
Since the start of June 2020, Japan Rail Passes have been issued with a QR code that allows you to use automatic gates to access station platforms.
You can find all our tips about traveling in Japan on our Japan by rail page.