Lessons 8 and Nine seem to boil down--after a lot of excessive descriptions of "what is a line" are eliminated--to this:
Lines connect points, and when "learning art," one should practice making lines. Freehand (lesson 8) and with the aid of a ruler
(lesson 9.) And sometimes one should hold the pencil or brush perpendicular to the paper and sometimes one should hold the pencil or brush so that its length goes in the same direction as the line.