This study guide provides a clear, structured, and exam-focused introduction to the topic of Physical Quantities and Units. It is designed to help students build a strong foundation in key physics skills such as SI base quantities, derived units, significant figures, uncertainty, scalar and vector quantities, vector operations, and exam-style vector problems. Each page is arranged in a visually clear format, combining definitions, worked examples, diagrams, quick-check questions, common mistakes, exam tips, and key ideas. The notes are especially useful for Cambridge AS Level Physics students because they focus not only on understanding the concepts, but also on how to apply them correctly in calculations and exam questions. The guide gradually moves from basic measurement and unit concepts to more advanced skills such as combining uncertainties and resolving vectors. It is suitable for classroom teaching, self-study, revision, and exam preparation.