Bootstrap's grid is an easy way to make your pages responsive.
The basic principle of Bootstrap's Grid system is that columns inside a row have different widths at different screen sizes. A column's width can be set serveral ways:
- Content Width stretches to fit in its content.
- Equal Width split evenly with the other columns.
- An integer between 1 and 12 the widths of all colums should add up to 12
For more information see the Bootstrap documentation.
You can use the 
Bootstrap Container, 
Bootstrap Row and 
Bootstrap Column Controls to create your own responsive grid.