I am new to this site. I see the email icon, at the bottom of a post.
When I click on it, it asks me to enter my email address, as well as the email address, of the person I want to contact. However, I don't know it.

I would appreciate if someone would explain.


That email link is a third party service, it simply forwards email independent of a mail service. Hmm, might be handy.

To contact a DaniWeb member, click on their name in the upper left of the post and you'll get an option to send a private message, via DaniWeb.

Yes use the PM feature. The mail button on posts itself is to send the content of the post (and a link to it) for someone to whom you think it may be helpful. Its not for contacting people with.