Bootstrap's grid system is its most popular feature. It allows developers to quickly develop responsive webpages. Respsonsive webpages are webpages that resize with respect to the screen size. HTML elements can be resized depending on the size of the screen.
For example, a developer may want one picture to take up the entire screen on a mobile device. On the other hand, he may want two (or maybe four) pictures display per row on larger screens. Bootstrap makes it quick and easy to implement this.
The Bootstrap grid system splits a screen into 12 columns:
Developers choose how many columns an element should span on extra small, small, medium and large devices.
Please review the Bootstrap example and its source code.