For usage documentation please visit https://doc.babylonjs.com/overviews/gui

To install using npm :

npm install --save @babylonjs/core @babylonjs/gui

Afterwards it can be imported to your project using:

import { AdvancedDynamicTexture } from '@babylonjs/gui/2D';

And used as usual:

// Some awesome code
// Creates the post process
let postProcess = new AdvancedDynamicTexture("adt", 128, 128, scene);
// Some more awesome code

For more information you can have a look at our ES6 dedicated documentation.