The scene graph

Three.js uses a scene graph data structure. A scene graph is commonly used by vector-based graphics editing applications and modern computer games, which arranges the logical and often spatial representation of a graphical scene.

It is a collection of nodes in a graph or tree structure.

A scene contains lights, meshes and groups of these.

Let's create a sphere:

const geometry = new THREE.SphereBufferGeometry(1, 16, 16);
const material = new THREE.MeshLambertMaterial({ color: 0x663399 });
const sphere = new THREE.Mesh(geometry, material);

To add this mesh to the scene, call:

scene.add(sphere);

sphere.position.set(1, 2, 3);

const DEG = Math.PI / 180;

// set rotation of the object
sphere.rotation.x = 45 * DEG;
sphere.rotation.y = 45 * DEG;

You can organize your objects in groups and then set the position and orientation of the group.

const group = new THREE.Group();
group.add(sphere);

group.position.set(1, 1, 1);

You can traverse through a scene or group via scene.traverse() or scene.traverseVisible().