Most students skip to Chapter 4 (Torsion). Don’t. Curtis assumes you know statics, but he reviews it with aircraft notation.
The text provides an analytical introduction to the stiffness method (Matrix Displacement Method). It teaches students how to assemble global stiffness matrices manually for simple structures. This is intended to demystify the "black box" behavior of Finite Element Analysis software like NASTRAN or ANSYS.
(Use consistent units; convert thickness/area to account for stiffener/skin distribution.)
Having the PDF on your hard drive is useless. The keyword is "work" – problem-solving, derivations, and failure analysis. Here is a week-by-week strategy to actually use Curtis’s text.