Oxygen Mini Tutorial
Columns are an important part of creating a modern responsive webpage. When the webpage is displayed on a larger screen, it can accommodate more columns and therefore display more data. Whereas if the webpage is displayed on the smaller screen size, less columns are used, and the content will be resized to fit the columns and still be easily readable to the user.
In oxygen, you can click on Add and Columns.
And it will show you the different column layouts that you use in your website. When you first create then the columns will be empty so it is up to you to populate them with the content of your choice. When you do, be aware of how the content would have to shift if the page is being built on a mobile device. (See: mobile responsiveness)