We must understand the principle ...

The basic premise is that we do not learn to write well if you do not know how to hold a pencil and move his fingers. For holding the pencil illustrations are clear, and are intended for left-handers as well. The "Practical information" at the beginning of the book should be read by parents carefully before putting the notebook in the hands of children.
To answer Suzy, for mobility of the fingers, the little coloring areas are much better than the supermarkets that encourage the child to move his hand instead of moving your fingers! This, the author might have had to explain as she explains holding the pencil.
We would also have appreciated more writing exercises, but these are easily reproducible on lined paper (3 mm by eye).