can trains pass on unitracks?

I think as a kid I was told that one train had to stop for another to pass and the stopped train had a way of moving off he tracks. Is that true or does there have to be two tracks for a train to pass and in the event of one track or a stretch were there is one track dispatchers have to notify another train to stop?

Trains need two tracks to pass each other. They can't move off the tracks. In the event that two trains need to pass each other, one will stop on a siding and hold until the other train or trains pass it. On most mainline tracks, there are sections of double track. This makes it much easier for tains to pass each other. Dispatchers control almost all "passing" on the railroad.

Dispatchers control all passing on main lines and sidings