Hi same here, I thought it was really simple, build two train stations, one at each end, add locomotives in both directions around freight cars and voilà, I had a back and forth train cargo bringing me resources from far away.
I was reluctant to go trains, since I used belts a lot, then I built 4 big train lines like this haha.
So, what are we supposed to do ? A huge loop all around the world, like in a child's room ?
Most trains I see go back and forth on their tracks :)