Thoughts

I wonder. What is the thing that motivates thinking.

I can for example, turn to a page of my math textbook and think nothing of it.
On other situation, I can turn to that same page, and starts to wonder what does the bunch of text/equations mean.

Well, yeah, I can certainly say that in the second case I put my thought on it as an answer.
However, that is where the problem is...

What is the process before that?
What is there between looking at sentences/equations and thinking about it?

Is there some sort of 'switch' that when turned on, ACTIVATES thinking? If there is, how do I turn on the switch?
In computer analogy..., how do I start writing on the input buffer?

If I know that, I can probably do what people call PAYING ATTENTION more effectively.