You need to create an instance of Twitter class like below:
// If you don't specify the IP address, DHCP is used(only in Arduino 1.0 or later). // fill in an available IP address on your network here, IPAddress ip(1,1,1,1); IPAddress gw(1,1,1,1); IPAddress snip(1,1,1,1); IPAddress dnsip(1,1,1,1); // Your Token to Tweet (get it from http://arduino-tweet.appspot.com/) Twitter twitter("YOUR-TOKEN-HERE"); // this was YourID:Password in 1.0.1
You need also to refer begin Ethernet library.
and compile, upload code on your Arduino Board.