gem install riemann-dash riemann-dash
Then open http://localhost:4567 in a browser. Riemann-dash will connect to the local host (relative to your browser) by default, and show you a small manual.
Riemann-dash takes an optional config file, which you can specify as the first command-line argument. If none is given, it looks for a file in the local directory: config.rb. That file can override any configuration options on the Dash class (hence all Sinatra configuration) as well as the Riemann client options, etc.
set :port, 6000 # HTTP server on port 6000 config[:client][:host] = 'my.ustate.server'