Google Remarketing is a marketing tool, offered by Google, which displays ads to visitors who've previously visited your site, as they browse the Web. You can easily set up a Google Remarketing campaign for your site.
To get your remarketing tag:
Sign in to your Google Adwords account.
Follow the instructions here to get your Google Remarketing code.
Copy the conversion ID next to google_conversion_id.
To add the Google remarketing tag to your site:
Go to your 'Settings' in the editor toolbar.
Select 'Site integrations' from the options on the left.
Locate the Google remarketing tag option and select 'connect'.
Paste the tag ID in the field.