There are slides devoted to this topic: Lecture 2, pp. 37-43
Read “The Pascaline of Blaise Pascal,” on the History of Computing site, to learn the story behind the Pascaline’s development, followed by a detailed explanation of how the machine performs addition, subtraction, multiplication, and division.
For another description and explanation of the Pascaline’s workings, read the “About Pascaline” page.
Watch “How the Pascaline Works” for a clear, animated explanation for how the Pascaline performed addition and subtraction. This animation also goes into detailed examination of how the machine’s gears interact.
Ifrah, Georges, The Universal History of Computing, 122-125