Be sure to give the keyword to the recipient so that they can decrypt the text. I suggest to use a safer way than email to deliver the keyword (chat, txt, voice maybe). To decrypt a text use the same way and press the decrypt button. None of the data you enter is saved or even being sent to the server, the encryption happens in your browser (via JavaScript).
This uses the super old Alpha Crypt by Joseph Myers and is not meant as a high security solution following nowadays standards. It might still be helpful for some needs like not wanting anyone else easily and directly read your message in plain-text. If you really want to share sensitive text, consider using apps like Threema or Signal.