Trading Networks start up

Hi,

I started learning TN concepts recently.

During the document processing in TN there is a statement, “the partner sends an XML document to the Trading Networks wm.tn:receive service.”

How exactly will the partner send files to that particualr service?
Will they send it to some physical location? or will they invoke the service?

Please clarify. Also kindly provide any tutorial link/demo would be much helpful.

Thanks.