How do you use Bootstrap's responsive design features?

Bootstrap's responsive design features allow you to create a website that adjusts to different screen sizes and devices. Here are a few ways to use these features:

1. Using grid classes: Bootstrap's grid system is built to be responsive. By using the .col-* classes to define the width of columns, you can create a layout that adjusts to different screen sizes. You can also use classes such as .col-sm-*, .col-md-*, .col-lg-*, and .col-xl-* to specify different column widths for different screen sizes.

2. Using responsive utility classes: Bootstrap provides a set of responsive utility classes that you can use to show or hide elements based on the screen size. For example, the class .d-none will hide an element on all screen sizes, while the class .d-sm-block will show the element only on small screens.

3. Using media queries: Bootstrap uses media queries to apply styles based on the screen size. You can use media queries to create custom styles for different screen sizes, such as increasing the font size on small screens.

4. Using Flexbox: Bootstrap 4 uses flexbox to create a responsive and flexible layout. You can use classes such as .d-flex, .align-items-*, .justify-content-* to create a responsive layout that adjusts to different screen sizes.

5. Using JavaScript: Bootstrap's JavaScript plugins are also responsive, which means that they adjust their behavior based on the screen size. For example, the navbar plugin will change from a horizontal layout to a vertical layout on small screens.

It's worth noting that with the use of the above features, you can create a website that adjusts to different screen sizes, and provides a great user experience on any device.