A "ping" is a reply posted for the purpose of bringing an article to the attention the recipients named on the "to" list.
To use Freep mail, select the pull-down menu on the "Destinations" box in the upper right hand corner of the forum. One of the options is "my mail."
You can also click on anyone's handle in a reply post and send a Freep mail. If you have messages waiting, a notice will appear in the upper left hand corner.
I shall Freep mail you right after posting this so you can see how the notice appears!