Menu appears just as normal list - bug or feature or setup error?

Hi, I am just starting to dig into sage, so please excuse me when I am not seeing the obvious…

I just installed everything like described, gulp seems to do its job without problems, however the resulting website has no menu at all - instead all the conifgured menu items appear as an ordinary list, not as the bootstrap menu that I expected. Actually I need to work on a custom menu, so this is not so totally bad right now, however I am asking myself if this is the expected result or if something is flawd with my setup. On some places i read something about a nav.php, but there is no nav.php in the tree of sage (got it git).

It would be great if anybody would like to give me a hint on how to proceed - is sage so basic - that I have to start to build the menu from zero?

Thanks for your attention!

OK, thank you for the hint, I just wanted to know if the nav menu is really missing or if my setup was wrong, I figured it out meanwhile, but anyway the linked video is very nice to watch! Thanks!