Every three.js program is built from a Scene and Camera passed to a Renderer that draws them to a canvas

Three.js structures browser 3D around three core objects. The Scene is the root of the scene graph — a tree that holds all drawable objects plus background and fog settings. The Camera defines the viewing frustum (what is visible and from where). The Renderer takes the Scene and Camera and draws the result onto an HTML canvas element. Nothing is visible until all three are wired together and renderer.render(scene, camera) is called. A common beginner mistake is adding objects to a scene but forgetting to position the camera away from the origin, making geometry invisible because the camera is inside it.

Examples

const scene = new THREE.Scene();
const camera = new THREE.PerspectiveCamera(75, window.innerWidth/window.innerHeight, 0.1, 1000);
const renderer = new THREE.WebGLRenderer();
renderer.setSize(window.innerWidth, window.innerHeight);
document.body.appendChild(renderer.domElement);
camera.position.z = 5;
renderer.render(scene, camera);

Assessment

Draw the data flow from Scene + Camera through Renderer to the canvas. Then identify what changes in the output if (a) camera.position.z is set to 0 and (b) renderer.setSize is not called.