The environment variables are strings with information about the drive, path or file name. There can be user environment variables or system environment variables. The user environment variables can be modified, added or deleted by all users, while only administrators can do this on system variables. With respect to syntax, they are normally inserted between % symbols.
For example, in order to access the environment variables in the case of Windows XP:
Double-click on System in the Control Panel.
In the Advanced settings tab, click on Environment variables.
Select the user or system environment variable you want to modify or delete, and use the buttons to add, modify or delete a variable.