Go to your Business Manager account: https://business.facebook.com
Pick your Ad Account.
In the most top-left mini-menu (9 dots), pick Events Manager
Pick the pixel you want to use (if you have more than 1)
Click on the blue Add Event button.
You can choose Use a Partner (eg. for integrations with Kajabi, Shopify, Squarespace, Wix, etc.) or Install code manually. Let's install the code manually.
Step 1: Install Base Code. Click on the green Copy Code button. This will copy your pixel base code. It will look something like this:<script>!function(f,b,e,v,n,t,s){if(f.fbq)return;n=f.fbq=function(){n.callMethod?n.callMethod.apply(n,arguments):n.queue.push(arguments)};if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';n.queue=[];t=b.createElement(e);t.async=!0;t.src=v;s=b.getElementsByTagName(e)[0];s.parentNode.insertBefore(t,s)}(window, document,'script','https://connect.facebook.net/en_US/fbevents.js');fbq('init', 'XXXXXXXXXXXXXXXX');fbq('track', 'PageView');</script><noscript><img height="1" width="1" style="display:none"src="https://www.facebook.com/tr?id=XXXXXXXXXXXXXXXX&ev=PageView&noscript=1"/></noscript>The green digits above are your pixel ID.For now, just save this code somewhere - you'll need it to complete #8 below.The pixel installation process continues at #9 below.
Place the pixel base code on every single page of your website.Login into your website. To add the base code, you can either: 8a. add it manually into every single page, or 8b. add it site-wide -- your website platform should enable adding a base code script in one place for all pages within your website. Look for options like: Tracking Code, Custom Scripts.This base code should be added in the HEADER area, between <head> </head> tags (you should be able to see these options).Some platforms will just ask for your Pixel ID and handle the rest. You'll find the pixel ID under the pixel's name in the Events manager.
Step 2: Enable Advanced MatchingNow, switch back to the Facebook's Business Manager, continuing #7 above.Set all options to ON.
Step 3: Add Event Code.It's now time to pick a page-specific event that you want to track.You can either use standard events or create your own custom events. You need to install this piece of code on a page that you want to track a specific event, eg. purchase, optin, etc.Event codes inform Facebook about the specific event that just happened for the person visiting this page. For example, on your order confirmation page you want to add an event that track purchases.On your subscribe-to-email-list thank you page, you want to add an event that tracks optins (leads or registration completed).See Additional links below for standard events or watch the next video to learn how to create a custom event.10a. If you added the base pixel code to every single page manually (8a)you have to add your event right after the fbq('track', 'PageView'); part. So now your full pixel code will look like this (note the green part):<script>!function(f,b,e,v,n,t,s){if(f.fbq)return;n=f.fbq=function(){n.callMethod?n.callMethod.apply(n,arguments):n.queue.push(arguments)};if(!f._fbq)f._fbq=n;n.push=n;n.loaded=!0;n.version='2.0';n.queue=[];t=b.createElement(e);t.async=!0;t.src=v;s=b.getElementsByTagName(e)[0];s.parentNode.insertBefore(t,s)}(window, document,'script','https://connect.facebook.net/en_US/fbevents.js');fbq('init', 'XXXXXXXXXXXXXXXX');fbq('track', 'PageView');fbq('track', 'MyCustomEvent');</script><noscript><img height="1" width="1" style="display:none"src="https://www.facebook.com/tr?id=XXXXXXXXXXXXXXXX&ev=PageView&noscript=1"/></noscript>10b. If you added the base pixel code site-wide (8b), you have to add the event tracking code manually to the specific page in the HEADER area (between <head> </head> tags) and it will look like this:</script>fbq('track', 'MyCustomEvent');</script>
Standard events you might want to use:

Additional links:

Specifications for Facebook Pixel Standard Events - types of standard events and which code to use

How to Install the Pixel