I was installed jdk 6.0 in my computer.But it did not work yet.I know it want to set the path.But I don't know how to do it.:-O Plz give me a:) answer quickly

Which operating system are you using? It's different depending on whether you're using Linux, Mac OS X or Windows.

Another approach is to use the full path to the command when using it so the OS doesn't need to look on the PATH for it.
On some OSes you could write a script or batchfile that has the full path in it.

Windows and Ubuntu Installation and PATH setup read here

Which version of Windows?

Which version of Windows?

Doesn't matter, steps are same. The only difference is where is Java folder located as this depends on type (32/64) you are installing.

Since I only have WinXP I have no idea of where to go to set Environment variables on Windows 7.
I click Start button, choose Settings, choose Control Panel, choose System, click Advanced tab and then click Environment Variables. Then I can add to PATH.

More or less same for Windows 7. As long you are Windows user with reasonable knowledge of OS you wouldn't have problem to figure that little differences. (Accessing control panel and navigation differ, but that is really just minor detail)

or less

It's the less part that can be a problem.

Or just open up the computer, right-click and select Properties.

There's a button there for editing environment variables on Windows 7. Can't remember if it was there in Windows XP as well ...