For Two Column layout, Use the structure of the layouts-two-column.html file.
Each of the layout options is provided below with steps you would need to perform in the layouts-two-column.html or index.html file:

Use below given attribute to set Two column layout.

data-layout="twocolumn"

How to add new menu items/change menu items?

In order to add, change or remove menu items from the left side navigation, simply edit in file Velzon/Ajax/default/index.html. The change would reflect in all the html files automatically. We are using gulp which would actually take care of including the Velzon/Ajax/default/index.html file content in the all html pages.