This code creates a scene, a camera, and a geometric cube, and it adds the cube to the scene. It then creates a WebGL renderer for the scene and camera, and it adds that viewport to the document.body element. Finally, it animates the cube within the scene for the camera.

import * as THREE from 'three';

const width = window.innerWidth, height = window.innerHeight;

// init

const camera = new THREE.PerspectiveCamera( 70, width / height, 0.01, 10 );
camera.position.z = 1;

const scene = new THREE.Scene();

const geometry = new THREE.BoxGeometry( 0.2, 0.2, 0.2 );
const material = new THREE.MeshNormalMaterial();

const mesh = new THREE.Mesh( geometry, material );
scene.add( mesh );

const renderer = new THREE.WebGLRenderer( { antialias: true } );
renderer.setSize( width, height );
renderer.setAnimationLoop( animate );
document.body.appendChild( renderer.domElement );

// animation

function animate( time ) {

	mesh.rotation.x = time / 2000;
	mesh.rotation.y = time / 1000;

	renderer.render( scene, camera );

}

If everything goes well, you should see this.