Okay, so imagine you have a really long train with lots of train cars. Sometimes, the train needs to go to different places and the train cars need to be separated so they can go in different directions.
But you can't just take the train cars apart anywhere, because the train needs to be safe and not just fall apart while it's moving. So, the train stops at a special place called a "dividing point."
At the dividing point, the train cars are uncoupled from each other using a special tool called a "coupler." Then, the train cars that need to go in one direction are moved away from the train cars that need to go in a different direction.
It's kind of like separating toys into different boxes: you have some toys that go in the blue box and some toys that go in the red box. Once you have sorted all the toys, you can take them where they need to go.
After the train cars have been separated, they are then re-coupled to their new trains and the journey continues. And that's how you divide a train!