Press the button to generate a pair of randomly chosen keys.
The public key will be posted in a public key repository where anyone can find it.
The private key should be known only to you.
Now type in a short message and enter one of the keys from above. Then press the button.
Pretend that you have received the encrypted message over the Internet. Now enter an appropriate decryption key and press the "Decode" button.
Hint: If you used one of the two keys generated in step 1, the other key works here.