It's true! There are no roads that go to Juneau. You have to get there by ferry system or by plane.
From Seattle (2 hours) or Anchorage (1 1/2 hours), you would be best using Alaska Airlines. From nearby cities such as Skagway, Haines, Gustavus, etc., small commuter planes are available.
The Alaska Marine Highway System or a charter company could be used.
Once you're in Juneau, the road system is adequate and there is a main highway approximately 45 miles long, known as Egan Drive, that follows the coastline.
Juneau image courtesy of alaska.org