Private messages.
Look to the top of your browser, for the icons that look like an envelope, a bell, a lightning bolt, and the search magnifying glass.
The envelope icon contains a link to your personal messages. Click on it.
To reply to a message to you, select reply, then type your message and send it.
Be sure when you initiate a brand new first message to someone, to check the box to 'allow others to join the conversation '. Otherwise they won't be able to reply.
Enjoy the site
@ARCO and good luck on your quest !