Using Iportal you, or someone else, can send trains to one another, either to a PC right next to yours in the same room, or across the world (provided that you both have the same locos and cars downloaded on both PC's).
Using Iportal you can also send your trains to another closed route on your route list, and when you open, the once closed route, your train will emerge on the new route.
You must name Portals and Iportals using the "?" button, and your partner must configure his Iportal to send/receive trains to/from your Iportal name(s).