Pixel installation and configuration takes place in 3 stages:
installing the main pixel code on the site;
configuring tracking events;
testing the correctness of the work.
There will be a unique pixel code for each Ads Manager advertising account. You can't copy and paste the first code you see.
How does it work?
When someone visits your site, the site code and pixel code are loaded. The system tries to match a site visitor with a social network user. If the system succeeds, the person is "caught", regardless of the device or the platform they use: a smartphone, a desktop, Facebook or Instagram. Now Facebook knows that this user has visited your site.