To start using the Material theme you need to install the vaadin-material-theme package using Bower.
To have the full benefit of using the theme, you should also use Vaadin Elements, such as vaadin-text-field, vaadin-button or vaadin-grid. You can install those using Bower as well.
After installing the theme package, import any element specific theme files you need. Here, we are importing the Material theme for vaadin-text-field.