Enter a password or private key in the first box. Tab out of this box after entry & notice this is transformed to a number which serves as the encryption key for the Diffie-Hellman algorithm.
Next enter your plain text (unencrypted message) in the third box. When you tab out of this, you will see the encrypted code (ciphertext) and the decrypted message (plain text). Next, go back and change the initial box (password) and note that the encrypted message changes in unpredictable ways. In an actual implementation, very large prime numbers are utilized to foil decryption efforts.