All you need is essentially a remarketing pixel code installed on all pages on your website. So that when users visit your site, they are captured into a “list” and then Google can target these users with ads after they left your website. We will help you install and test the remarketing tag during the account setup.
For e-commerce sites, a more complex setup is needed, where the tag will capture the product information and send back to Google Ads to match the user with the relevant product ads.