Step by step tutorial

Sorry, I'm a newbie with drupal, CSS, HTML

I don't understand how this module works.
I mean, I download and active it, and that's okay.
In module configuration I set:
Menu -> main
Menu class/id -> navbar (i'm not sure, i'm with bootstrap 3. Where I can found my main navigation menu id?)
Menu item selector -> empty (I can't change it)
Title -> Main
Tag -> h2 (this means that it will scroll to elements with h2 tag, i think)
Homepage -> this page as my homepage

Now, When I go to mysite.org/single-site-page there is always a "Page not found" error with all the other elements of homepage.

First question: Why this error? How I can fix it?

Then, following the readme instruction, I go to structure -> menus and to Main navigation ('cause I've set this menu in module configuration)

Second question: What I have to do? If I create a new link I can't set the class.

Can you explain me, please?