Mental space is like having a room in your brain where you can store and think about different things. Imagine you have a toy box with lots of different toys inside. You can take out one toy to play with and put the others away for later. Your brain works the same way – it can focus on just one thing at a time, but you can also switch your attention to different toys or topics as needed.
For example, if you are playing with your toy cars, your mental space is focused on imagining and driving the cars around. But if someone comes into the room and starts talking to you about something else, you can switch your mental space to focus on the conversation instead.
People use mental space all the time without even realizing it. When you are trying to solve a problem, you might put all your mental space into thinking about different solutions. Or when you are reading a book, your mental space is focused on understanding the words and imagining the story in your mind.
So, mental space is basically like having different rooms in your brain where you can store and think about different things. And just like in real life, you can change your focus and move to a different room as needed.