This book introduces the content of Descartes's famous book Geometry in simple language and modern mathematical symbols, aiming to help beginners who enjoy analytical geometry understand Descartes's mathematics as soon as possible. In order to achieve this goal, this book also includes a brief introduction to Descartes himself, ancient Greek mathematics, the Pappus problem, Apollonius' mathematics, and the history of Root Formulas for Univariate Equations, etc. Finally, the compiler's interpretation of Descartes’s mathematics is also included.