This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
It means that either you don't have the javac compiler installed on your machine, or more likely you have not set up your PATH environment variable to include the your JDK's bin directory. You need to tell your operating system where to look for an excecutable called javac and you do that by setting the PATH.