How do I hide the drawer when the user clicks on an item? Or when a button is clicked?
I believe you can remove the is-visible class from .mdl-layout__drawer. I tried modifying a codepen example from their site: demo. My pure javascript event binding is rusty, but as I mentioned, you just need to remove the .is-visible class from the drawer.
The code I provided was for v1.0.0 of mdl and is not actual anymore. Starting at v1.1.0 there is a public API provided for toggling the drawer, as described in Benjamin's answer. If you're between v1.0.6 and v1.1.0, have a look at idleherb's answer.