I mean like how do we really gather our ideas or our thoughts to think about what we want to think about. Not sure if I worded that correctly.
For example, if you ask me what does apple reminds me of, then I can start with an actual red/green apple, then the company apple, then their iPhone, then it's competitor Android, then finally my own Samsung phone. But it doesn't always end up as my own Samsung phone. In other instances, I can start with an actual red/green apple, then relate to fruits, then strawberries, then finally strawberry milkshakes. I got no clue how my thought process works.
Sometimes when I have something in my mind, like a person or an event, everything would bring me back to that person or event. Like when I had to go for an interview, I tried to not think about it and get a good night's sleep. So I tried to think about random things by one after another, I just ended up thinking about my prep questions for the interview.
I suppose this is where the saying "trains of thoughts" work out since it looks like there are many trains of thoughts in my mind and then each train have many carts that also have ideas or other thoughts. Or "Chains of Memory" where each memory is linked together somehow and intertwined. (Reference to the game Kingdom Hearts.)