@Override
  public void simpleInitApp() {

    /* A simple textured cube -- in good MIP map quality. */
    Box cube1Mesh = new Box( 1f,1f,1f);
    Geometry cube1Geo = new Geometry("My Textured Box", cube1Mesh);
    cube1Geo.setLocalTranslation(new Vector3f(-3f,1.1f,0f));
    Material cube1Mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    Texture cube1Tex = assetManager.loadTexture("Interface/Logo/Monkey.jpg");
    cube1Mat.setTexture("ColorMap", cube1Tex);
    cube1Geo.setMaterial(cube1Mat);
    rootNode.attachChild(cube1Geo);

    /* A translucent/transparent texture, similar to a window frame. */
    Box cube2Mesh = new Box( 1f,1f,0.01f);
    Geometry cube2Geo = new Geometry("window frame", cube2Mesh);
    Material cube2Mat = new Material(assetManager, "Common/MatDefs/Misc/Unshaded.j3md");
    cube2Mat.setTexture("ColorMap", assetManager.loadTexture("Textures/ColoredTex/Monkey.png"));
    cube2Mat.getAdditionalRenderState().setBlendMode(BlendMode.Alpha);  // activate transparency
    cube2Geo.setQueueBucket(Bucket.Transparent);
    cube2Geo.setMaterial(cube2Mat);
    rootNode.attachChild(cube2Geo);

    /* A bumpy rock with a shiny light effect. To make bumpy objects you must create a NormalMap. */
    Sphere sphereMesh = new Sphere(32,32, 2f);
    Geometry sphereGeo = new Geometry("Shiny rock", sphereMesh);
    sphereMesh.setTextureMode(Sphere.TextureMode.Projected); // better quality on spheres
    MikktspaceTangentGenerator.generate(sphereMesh); // for lighting effect
    Material sphereMat = new Material(assetManager, "Common/MatDefs/Light/Lighting.j3md");
    sphereMat.setTexture("DiffuseMap", assetManager.loadTexture("Textures/Terrain/Pond/Pond.jpg"));
    sphereMat.setTexture("NormalMap", assetManager.loadTexture("Textures/Terrain/Pond/Pond_normal.png"));
    sphereMat.setBoolean("UseMaterialColors",true);    
    sphereMat.setColor("Diffuse",ColorRGBA.White);
    sphereMat.setColor("Specular",ColorRGBA.White);
    sphereMat.setFloat("Shininess", 64f); // [0,128]
    sphereGeo.setMaterial(sphereMat);
    //sphereGeo.setMaterial((Material) assetManager.loadMaterial("Materials/MyCustomMaterial.j3m"));
    sphereGeo.setLocalTranslation(0,2,-2); // Move it a bit
    sphereGeo.rotate(1.6f, 0, 0);          // Rotate it a bit
    rootNode.attachChild(sphereGeo);
    
    /* Must add a light to make the lit object visible! */
    DirectionalLight sun = new DirectionalLight();
    sun.setDirection(new Vector3f(1,0,-2).normalizeLocal());
    sun.setColor(ColorRGBA.White);
    rootNode.addLight(sun);
  }
Sample 6 - how to give an object's surface a material and texture.
How to make objects transparent. How to make bumpy and shiny surfaces.
jme3-examples/src/main/java/jme3test/helloworld/HelloMaterial.java