These are examples. 

This explains defaults:
Padrino.run! # with these defaults => host: "127.0.0.1", port: "3000", adapter: the first found

This should explain expert usage:
Padrino.run!("0.0.0.0", "4000", "mongrel") # use => host: "0.0.0.0", port: "4000", adapter: "mongrel"