You can find your navigation bar in 'Website', then 'Settings'.
Firstly, you can toggle the navigation bar on or off. You may want it off if you only want your customers to see the page you link them to, or if you are embedding a specific page and have no use for it,
In the lower section, you can tick which tabs you want to appear in your navigation bar.
Here is how the navigation bar looks! Each tab is clickable and takes the customer to a page of your site.