I wrote down CLASSPATH and PATH in my system variables already.
The CLASSPATH's value is %classpath%;. And the PATH's value is %path%;C:\Program Files\Java\jdk1.6.0_20\bin
I'm not sure if there are any errors in that above, so I just included it.
After this, created my source file, saved it in C:\Program Files\Java\jdk1.6.0_20\bin as MyFirstApp.java. So I open command prompt, enter: javac MyFirstApp.java
This is what comes up:
javac: file not found: MyFirstApp.java
Usage: javac <options> <source files>
use -help for a list of possible options