Secure Text -AES256 Encryption

I love the concept, I believe this app is 100% legit despite the low amount of downloads. Moreover, it is truly secure in every sense of the word. I just have one question for the developer- When going to decrypt how does it work? I understand that you type a message- encrypt that message, save the key, then copy the encrypted message and send that to the receiver, then they must use the same key to decrypt my message- but how am I supposed to do that exactly? Like what are the steps?