>>529227770
The blogpost is pretty much all you need.
https://factorio.com/blog/post/fff-395
Basically the train scans its cargo and will change the wildcard to the icon of that item. So in my case (Wildcard)Unload becomes (Iron)Unload when it picks up iron and will happily deliver to that station.

Here's the dead simple setup I use for basic ore delivery. Every single pickup station in the group is named 1-4 load (1 loco 4 wagons obviously)
All unload stations have their resource icon in the name. When there's no stations available trains park in the depot and wait. You can get fancy and add fuel stops but I find it far simpler to just fuel them at the unload stations.

Hope that helps.