To use remarketing on the Google Display Network, you may want to choose "Display Network only - Remarketing" as your campaign type when you create your campaign

How remarketing works

Remarketing can help you reach people who have previously visited your website as they visit other sites on the Google Display Network or search on Google. Using remarketing, you can show these customers messages tailored to them based on which sections of your site they visited.

To start using remarketing, you need to add the remarketing tag, a small snippet of code that you get from AdWords, across all your site pages. Many sites have an identical footer for all pages, and this remarketing tag could be placed there.

Once you've added the remarketing tag to your site, you can create remarketing lists for any of your webpages. For example, you could create a remarketing list for visitors to your most popular product category. The remarketing tag tells AdWords to save visitors to your "Popular category list." When people visit that page, their cookie id is added to the remarketing list.

Then, you create an AdWords campaign with a specific message to show only to people on your "Popular category list" while they search on Google or browse other Display Network sites. Your remarketing messages won't be shown to people who are not on the list.
Because the remarketing tag is on all of the pages of your website, you can develop more detailed audiences. For example, you could create lists not only for your most popular product category, but also for each of your other product categories or your shopping cart.

How to Create a Remarketing List?

•    To run a remarketing campaign, you'll need a collection of cookies from people who visited your site, also called a remarketing list.
•    Your remarketing list can include people who visited a certain page on your site, and you can also create more advanced lists using templates and the rule         builder.
•    Go to the "Shared library" in AdWords to create remarketing lists. Once your list is created, you can apply the list to your remarketing campaigns.

About creating a list

If you want to run a remarketing campaign to show ads to people who have previously visited your site, you'll need a remarketing list. A remarketing list is a collection of cookies from people who visited your site. Creating the list is one of the most important steps in setting up a remarketing campaign because you'd use this list to target your ads. You can start creating lists at anytime, but they'll only start getting visitors after you've placed the remarketing tag on your site.
Create as many remarketing lists as you'd like. Once you've created lists, create new campaigns and add your lists to your ad groups.

•    To use remarketing on the Display Network, select "Display Network only - Remarketing" as your campaign type. The default settings in this campaign type can help you achieve better performance.

•    To use remarketing lists for search ads, select "Search Network only - All features" as your campaign type. Remarketing lists are not available for "Search Network only - Standard" or "Search & Display Networks - Standard" campaigns.

Note: Before you create your list, read about remarketing strategies and best practices to learn what kind of list best suits your goals.