The Bar is a feature that allows you to display a message at the top of site. The bar can appear almost immediately or after a few seconds.
You can have more than one bar where you display a certain bar on some pages and different ones on others, or none at all. The bar also has the facility to change what it displays based on the size of the display.
So for example you may show a phone number on a desktop,but change this to a click to call button on a mobile phone.