If Your Are Using Shopify
If you are using Shopify and have downloaded the app from the Shopify App Store, there is nothing more you need to do. Simply activate your banner and you're all set.
How To Manually Install The Code Snippet
Start by creating a banner. After you've customized and configured your announcement banner, click on the "Install Code Snippet" button in the top right area of your screen.
Then Copy the script tag that is displayed.
Paste the snippet into the <head></head> of your website.