The "HOW IT WORKS" link in the header of
edx.org (
www.edx.org/how-it-works) is not part of the default Github design.
The issue seems to be not about theming, but "web routing" : the error is telling you "I don't know what view.html to load for the /how-it-works url".
Are you making a microsite for the official
edx.org ? In that case, they may have this on their official platform, the theme is just not compatible with the Github platform.
If it is for a non-official platform, you should declare the new view in the url.py file of the LMS (
https://github.com/edx/edx-platform/blob/master/lms/urls.py ), or maybe theming allows for an additional url.py in the theme directory, but I never used that feature.
Marceau