You can install as others regular WordPress plugin. No different way. Please see on installation tab.
Header Promo is Packed with huge numbers of features allowing you to achieve your goals.
Customize the header promo to your style. Change colors and background colors.
Show action button with custom text and custom colors and hover colors
Display text(message) of header promo. With the styles of the text.
Display the countdown for the promo. And style the countdown.