Java around the world

I'm running xp home. I downloaded JDK 6 and installed the program. At the Sun Developer Web Site i started taking the first lesson called "Hello World." I used note pad, wrote the very simple code, and saved the code as directed in a java file. I brought up a comand prompt using the run comand, switched to the java directory, and located my file. I then attempted to compile the program using javac but got a statement that javac was not recognized. I went to the help area of the lesson and it said i needed to point windows to the compiler. It said I could do this two ways. I tried both but neither works. How do I know if the javac file is okay? If it is okay why isn't it working? One of the methods suggested was to enter the path in the runtime enviornment. When I opened that window there were four lines and I didn't know what to put on each line so help with that might solve this. I really want to learn this stuff but there is a very large brick wall. Help!