2 trains collide on same track, what to do?

[factoriobiker]

Do I have to destroy one of them?
How to fix so they do not collide, they share a part of the main track but different stations

[Kyralessa]

You need to use train signals so they don't collide (as well as have at least one double-tracked section for them to pass each other, or a loop at at least one end.

Here's a good place to start learning how train signals work:

https://wiki.factorio.com/Tutorial:Train_signals

[TheEnemy42]

Have a look at the in-game tutorials. They actually do a pretty good job of explaining how trains and train signals work, along with some exercises to help you understand the nuances. They're available in-game using the tutorial button above the minimap.