Starting to use functionalities like Google Analytics, Google Tag Manager or Facebook Pixel usually requires that a small script (piece of code) has to be added to your website's header or footer section. You can do this yourself, by using Simple Header Footer HTML plugin, which is free open source plugin made by Seravo:
Go to Plugins-section in WP-admin
Install and activate Simple Header Footer HTML plugin
Go to Settings > Simple Header Footer HTML
Add your code snippet in the right place and Save changes.
