How does website speed impact SEO?

Reading a blog is easy. When you build your own blog then you may face several challenges. As a non-techie, I am overwhelmed by Google Search Console, analytics, tag manager, sitemap, and many more. Right! here I am facing an issue with website speed.

I have tested my website on GTMETRICS and Google Page Insights.

In Gtmetrix, the first contentful paint load at 896 ms and fully loaded at 1.8s. And the overall grade is "A".

In Google Page speed insights, the first contentful load time at 2.7s. And the overall score is 49.

Whats should I do now to improve my score on Google Page Speed Insights.

One more additional question, how to index categories on Google, Is there any important factor in indexing categories?