Hi there, Mark, and welcome to Google Community.

If you want to know how to send PMs, first click up above on "You have no messages" or "You have ... PMs".
That's a link to your PM inbox. There, you can click on New Post.
Then, you enter your message, the subject of the PM and the username of the person you want to send the PM to.
Then click Send or Submit, or something like that.
Hope that clears your question.