what you need to do is: you need to add the path, to do that, you right click my computer icon on the desktop, you then go to properties, from there you go to advanced, from advanced you go to Environmental variables, under System variables (in blue color), you double click path. at the end of you path you put a sermi-colon(, the you add your path, e.g if you using java 6(or jdk 6), you type in: C:\Program Files\Java\jdk1.6.0\bin; then click on OK, OK again, Apply, OK, then go to command, if you class is in c: you need to move to the c drive, this is how it is supposed to look: c:\> then type javac HelloWorldApp.java

Hope this will help