Understanding Bootstrap grid system !
It is following the newspaper 12 column layout style.
Choosing the Column in the layout by specifying the coloum
For Mobile screen automatic size change and stack into row wise, one below one. Re-size the browser to undersand this behaviour.
Ordering the column :
Nesting the columns using nested section tag !! Important concept - to layout the blog or webpage. Hint: Check where the fist div tag is getting closed !
Adoptive Sizing for the container !! Based on device width !!