Little Boat,
I apologize for the delay in replying to your post.
In the Level I manual that I have, Master Lin states:
"Visualize a transparent energy column of beautiful colors running from the top of the head to the bottom of the torso. While moving the hands, visualize the energy moving up and down the transparent column. Visualize the channels in the torso opening completely."
This is your guidance, to work with. Everyone, will proceed, in their own way. If I define "my way" of seeing it, it would greatly limit you, in finding your way of seeing it.
Let these words create an impression for you, or just a sense of something. Go with whatever your first impression is. If you have none, just do the exercise, and relax into it like a warm bath. It will 'still work for you', you won't miss out on the health benefits of the exercise, and you will make progress with visualization over time.
love,
gallen