There are 3 main button types described in material design. The raised button is a standard button that signify actions and seek to give depth to a mostly flat page. The floating circular action button is meant for very important functions. Flat buttons are usually used within elements that already have depth like cards or modals.
<a class="waves-effect waves-light btn">Stuff</a>
<a class="waves-effect waves-light btn"><i class="mdi-file-cloud left"></i>button</a>
<a class="waves-effect waves-light btn"><i class="mdi-file-cloud right"></i>button</a>
<a class="btn-floating btn-large waves-effect waves-light red"><i class="mdi-content-add"></i></a>
When you use a button to submit a form, instead of using a input tag, use a button tag with a type submit
<button class="btn waves-effect waves-light" type="submit" name="action">Submit
<i class="mdi-content-send right"></i>
</button>
This button has a larger height for buttons that need more attention.
Button button button
<a class="waves-effect waves-light btn-large">Button</a>
<a class="waves-effect waves-light btn-large"><i class="mdi-file-cloud left"></i>button</a>
<a class="waves-effect waves-light btn-large"><i class="mdi-file-cloud right"></i>button</a>