Facebook Remarketing works by tracking website visitors back to Facebook, where you will show them your ads. To track website visitors, you have to install a tracking code called “Facebook Pixel” on your website.
Start on the ads manager. Click on the main menu icon on the top-left, and then click on the “pixels” option under “measure and report”. Now click on the “add new data source” button and select “Facebook pixel”. Enter a name for your new Facebook pixel in the “pixel name” field and click on “create”. Your new Facebook pixel is ready. Now you have to install it on your website.