Just open your wallet and send 0.001 Hive to the mentioned account.
When you send Hive/HBD to someone, you have the possibility to add a Message to it by adding it into the "MEMO" field.

To send an encrypted MEMO, you NEED TO SET a # IN FRONT of your message, like:

#thisistherightword

Both sides will be able to read this message with the "MEMO-Key".