Setting up your PATH variable.

This video explains how to set your PATH variable on Windows XP. This video explains how to set up the JDK, however, it also applies to anything else.

For Windows XP:
Go to the start menu. Right click on My Computer and select "Properties". Select the "Advanced" tab. Click the "Environment Variables" button. Find the "Path" entry and double click it. Append a semicolon to the end if it's not already done and simply append the location of your JDK's binary directory to the end. For example, if you're using JDK 6u21, you would add ";C:\Program Files\Java\jdk1.6.0_21\bin" to the end.

For Windows Vista and 7:
Go to the start menu. Right click on My Computer and select "Properties". Select the "Advanced System Settings" link. Click the "Environment Variables" button. Find the "Path" entry and double click it. Append a semicolon to the end if it's not already done and simply append the location of your JDK's binary directory to the end. For example, if you're using JDK 6u21, you would add ";C:\Program Files\Java\jdk1.6.0_21\bin" to the end.

For (most) Linux:
Use "export PATH=$PATH:/path/to/jdk/bin". The vast amounts of places your JDK could be located prevent a rock-solid path. Also, most of the time if you install JDK via a package manager, this is done for you automatically.

To compile your code, use the "javac" command.