“Today I was reading of the ‘ vacuity’ of the form and non form, and how is difficult to understand the concept of it. I did not get which kind of enquiry should be done”.
Do not be so bothered about enquiry, it is simple.
You are not the body because it is an object that you SEE
You are also likewise not the mind because that too is objective.
What remains that is witnessing the appearance and disappearance of these two is what you are, very simply you are Awareness.
As awareness you can only be aware of yourself directly without any means or techniques etc
If attention is able to remain aware of this awareness all else will drop into place without effort and if attention is not able to do this it is simply not yet time for this to be steady, no effort will bring it about.
You are already Awareness, there is nothing to be added.
If there is a problem at all it is because it is too obvious and simple and the mind tries to DO it LOL