Learning.

Valerian watched the old man perform some basic actions in forging, and he thought, this forge was like a body, and the things related to forging were placed all over the place. If you need something, you can move it to the other spot. 

Like the material on the shelf, it can be moved over to the anvil and the furnace. So, if you think of the human body as the forge and the mana inside as the material, it would mean that the mana was stored all over the body and can be moved to different places, like channeling through the eyes, and the muscles. 

Valerian understood this, and just as he wanted to try it out Master Fern said, "See, a lot of people say that strength originates from muscles and certain points in the limb. However, they are not completely correct. The most optimal way to draw out strength is to use the entire body in one fluid motion. Observe my movements."