Action mailer receive email

I am following this rails guide But i am not able to understand what should it means
“Configure your email server to forward emails from the address(es) you would like your app to receive to /path/to/app/bin/rails runner 'UserMailer.receive('.”
Is there any screen-cast which explain these things ???

Please do not reply to me privately but to the mailinglist!

receive to |/path/to/app/bin/rails runner 'UserMailer.receive('|.
where i should run this command and where define outgoing server
configuration ???

This totally depends on which MTA/MUA you are using, you need to
configure it in the MTA/MUA you are using and how you do it totally
depends on the software uised. Perhaps someone else is able to help you
after you have provided necessary information.

which is completely irrelevant to the question of *receiving* mail...

good point, deleted the post.