This script is copied from http://www.tero.co.uk/des/code.php.
If you enter a 24 byte (character) key below it will use triple DES, or else it expects an 8 byte key for single DES. If you enter an 8 byte input vector it will use CBC mode, or else ECB mode. When encrypting, the result will be displayed in hexidecimal.
When decrypting, the message is expected to be hexidecimal. And you can copy back the result into the message to encrypt, then decrypt the same thing. Because of the conversion to hexidecimal and the padding DES adds, the encrypted result will always be at least twice as long as the original message.