WordPress can be an imposing environment for new developers. The barrier to entry is low — you can accomplish a lot by pasting snippets into your theme’s functions file — but it doesn’t take long to realize that WordPress is an enormous machine full of moving parts. Every page load requires a sequence of thousands of tasks that run in a specific order, and any code you write has to fit into that order. If you get the order wrong, your code might not run at all, or worse, it could bring down the entire site with a “white screen of death.”
WordPress provides developers with “hooks” that allow us to run our code at specific times.