This navbar was originally built by someone in the Coffeecup staff, and it has a tutorial with videos here. You will find everything needed to build it yourself on that page.
However, if you need it real fast, you can download it from this page.
Below there is a second variant which has the menu items centered. This menu also stays as a 'hamburger' menu through the middle viewport up until the large viewport kicks in after the 2nd breakpoint.