I follow a few "low-end" Facebook groups focused on marketing and best-practice advertising. I'm not sure why I do because the misguided information only further fuels my disdain for that segment of the marketing community that really doesn't have a clue what they're doing. Anyhow, one of the questions that pops up from time-to-time is how to enter the Facebook tracking pixel into the head of a WordPress website. Since you'll be using the pixel on every page of your website, using the
wp_head action to render the code is appropriate.
Only use a plugin if you absolutely need additional features and functionality, and never just add the code to a core file (around half of the clueless contributors to the thread in question tend to advocate this nonsense). If you're a client, our full-featured plugin includes all the pixel-related features you'll ever need; activate from your control panel.
Copy and paste the WordPress function into your theme's
functions.php file or, if you sensibly have one installed, your custom functions plugin.