All pad-specific settings are loaded from a file called "padinfo.json" -- by default etherdump looks in the current directory. Make a copy of padinfo.sample.json to start one. Make sure to check that the URL and port settings are correct, and to paste the correct apikey here!
Etherdump is useful as a means of dumping the contents of etherpad to files, as a way of opening up the contents of the service to other services / methods / uses / tools / situations. (Files also of course allow for archival tools / methods)