Free-Body Diagram
Also called FBD, Force diagram
A free-body diagram shows one chosen object as a point or box with an arrow for every force exerted on it by something else, and nothing else on the page. It is the step that turns a described situation into an equation.
Drawing forces on the object of interest, and only that object, is the most reused skill in AP Physics 1: learning objective 2.2.B asks for it by name, and later units keep calling on it.
Every arrow needs a second object. Forces are interactions, not possessions. A force exerted on an object is always due to that object interacting with another object or system, so every arrow survives two questions: what is the other object, and what kind of interaction is it? If you cannot answer both, the arrow is not a force and does not belong.
That single test removes most invented arrows. There is no force of motion, no centrifugal force pushing a turning car outward, and no inertia arrow. Naming each force with both nouns, as in "the force of the table on the book", makes the test automatic.
Only forces on the body. Forces the body exerts on other things belong on those things' diagrams. That is the discipline that keeps Newton's third law pairs from cancelling themselves by accident.
For the step-by-step routine, the force inventory and the errors that break diagrams, use how to draw a free-body diagram, then build a few yourself and get checked in the free-body diagram builder.