Buttons are used as CALL TO ACTION, available in different sizes and states.
The basic button has 7 different states - primary, secondary, success, danger, warning, light & dark.
The outline button has no background color. You can use it as secondary call to action.
The link button has anchor tag which enables link action.
These buttons have icon which enhance the overall experience.
Buttons are available in 2 different sizes - btn-lg & btn-sm
Utility classes will provide more customisation - .btn-disabled class which makes the button disabled and .btn-shadow which provides a little elevation to the button.