Once the tag is published in your website, the next step is to create remarketing lists in AdWords
A remarketing list is a collection of cookies from people who visited your site. If you decide to set up a remarketing campaign, this is the list you'd target your ads to. Creating the list is one of the most important steps in setting up a remarketing campaign. You can start creating lists at anytime, but they'll only start getting visitors after you've placed the remarketing tag on your site.
For more information Go with this link,
Before you dig into the technical details of creating remarketing campaign and all, you need to understand what it is and whether it would be an effective way specific to your business to re-target the people which you want.
Please note that remarketing is going to show the ads to the same users who have visited your site earlier also and whether it makes sense to target them again or not. And if you feel like it would be a good way, then there are many ways in which you can create custom combination of remarketing lists and based on that, target your users separately showing remarketing ads.
Otherwise, you can create the remarketing tags in Adwords and implement it in your website using Adwords.
My 2 cents!