It’s a video tutorial of article “Understanding the Bootstrap 4 Grid System” – https://designmodo.com/bootstrap-4-grid-system/
Grid systems enable us to properly organize website content. Dividing the screen into multiple rows and columns is the best way to create a variety of layouts for any kind of website.
Bootstrap’s grid system has a division of columns ― up to 12 in each row. Each column width varies according to the size of screen they’re displayed in. Bootstrap’s grids are responsive and each rows may collapse at a certain breakpoints or can displayed fluidly across different viewports.