Projects in this class are in the C programming language.  You can download the free software from http://arduino.cc  This helps you create programs (called sketches).  Then you can compile and upload the sketch from the Arduino software to your Arduino board.

If you are using CrowdBot to learn Arduino over the internet, download the Arduino software and check that your program compiles.  This helps catch errors.  Then enter your program on http://mapmeld.appspot.com/crowdbot  for the class

There's also a popular language for the Arduino called Processing.  Processing programs run on your computer while controlling an Arduino that is connected by a USB cable.  You can download the free software from http://processing.org/download/ and prepare your Arduino by following the directions on this page: http://www.arduino.cc/playground/Interfacing/Processing