What Google measures
Three things, and they're all about what the visitor feels. How long until the main part of the page shows. Whether things jump around while it's loading, so you tap the wrong thing. And how quickly it reacts when you do tap.
You can see your own numbers for free in Search Console, under the page experience reports. They come from real visits to your site rather than from a test on a fast connection, which is why they're worth more than most speed tools.
Why it matters more for a trade
Your customers are outside. They're in a driveway, in a truck, at a job, on a phone with a weak signal and one hand free. That's the hardest case a website gets, and it's the normal case for you.
A page that takes eight seconds there loses most of the people who asked for it. They go back and tap the next company, and you never know it happened, because a visitor who left doesn't show up as anything you can feel.
What makes a contractor site slow
Almost always photos: full size pictures straight off a phone, eight of them on the gallery. After that it's add-ons, the chat widget and the review slider and the tracking scripts, each loading its own pile of code before the page can settle.
The fix for both is unglamorous. Save photos at the size they show at, load the ones below the fold only when somebody scrolls, and keep the add-ons to the ones you'd miss.
What speed can't do
It can't put you in a town your site says nothing about. Google is clear that having the content somebody wants beats being quick, so a fast site with five pages still only covers one town.
So treat speed the way you'd treat a clean truck. It matters, people notice, and it isn't the reason anybody hires you. Clear the floor, then spend the effort on the pages.