I believe trainers can tell you about what other trainers can teach you.
If you want to go to Stormwind from Darnassus, take the boat from Auberdine to Menethil. Exiting east of Menethil, follow the path all the way to the south-east part of the zone, until you enter a tunnel in the mountain. If you are low level, you might die a few times, but just go back to your body and keep going. It's called a corpse run :P Do it naked so your gear doesn't get broken.
After the tunnels in the mountain, you keep going south. Always follow the road. Eventually there will be a tunnel that will take you to the dwarf starting are Dun'Morogh. I'm fairly certain there are signs along the road to tell you which tunnel take.
In Dun Morogh it's easy. Once again just follow the road, to the west, until you get to Ironforge. In Ironforge, take the Tram. It's on the map :)
I hope all of this is right :P