Hi all, @macchiata and I noticed that there are some important steps missing in this tutorial:
First of all, you'll need to separate your public and private keys. If you do NOT do this, other people will be able to view all your encrypted messages when you share your key. To do this, open your key file with Notepad, COPY ONLY THE PUBLIC KEY into a NEW text file, and save the new file as your Public Key.
Secondly, you'll need someone else's public key to send an encrypted message to that person. When you have their key, you need to import the file to GPA. Then, when encrypting a message, you need to select the other person's Public Key, and sign the message with your own Private Key. Only then will the other person be able to decrypt the message you sent them.
Please let me know if I should make an instruction video, because it can be quite difficult to take in all at once. :)
Steem on!