Bootstrap provides a responsive grid system that appropriately scales up to 12 columns as the device or viewport size increases. To create a responsive layout using bootstrap 12 column structure these points need to be considered

☛ All the rows must be placed inside of a div having class .container or .container-fluid

☛ Create a div having class .row to group column

☛ Add columns inside row as immediate children of row

☛ Place all content inside columns

☛ There are pre-defined classes for columns. These classes are col-md-*, col-sm-*, col-lg-*, col-sx-*where * represent number from 1 to 12. These classes take effect as per viewport of the device.

if a row has column with class .col-sm-4 then it mean it will occupy first 4 column for small device and full width in extra small device.

similarly column with class .col-sm-8 will occupy next 8 column in the row and full width for extra small device.