12v relay help

Alright im new here and im decently new to arduino. what im working on is a 6 legged robot and the legs are run by two 24 volt wheelchair motors. im having a real issue on finding a way of wiring the relay to the arduino using a TIP120 transistor. please help

for those interested im following this for the build: http://www.instructables.com/id/Hexabot-Build-a-heavy-duty-six-legged-robot/
the guy didnt include directions on electronics. i mean he did but they are not detailed enough for a beginner like myself.

A quick Google search for Arduino relay TIP120 turned up this:
http://bildr.org/2011/03/high-power-control-with-arduino-and-tip120/