I found on RIM website "http://www.blackberry.com/devicesoftware/entry.do?code=maps", does it only provide Map Application but not Map? If not map, where & when to get the map?

does it mean when travel to someplace, 8800 will download the local map automatically?

You need to subscribe (pay for) a Navagation service to get the maps from what I understand. Like TelNav

That is BlackberryMaps. Your device should have that already installed and it's free to use (if you have a data plan.)

Blackberry maps will download maps for you automatically.