SEO simply "translates" your website into language that's easily understood by search engines -- so users see your pages when they go hunting for offers, products, services, information or answers to specific questions.
The exact formula used by Google and Bing is subject to debate. RankBrain, content and links that point to your site are three of the biggest ranking signals. But other factors play their role, too.
Keywords used to be ... well, key. But then content became king.
You still need keywords. Two mistakes that novices and “experts” alike continue to make? Stuffing keywords and targeting the wrong words.
Stuffing aims to trick the engines by using an exact keyword phrase in an unnatural frequency.
Do that, and the engines will penalize you.
Have a keyword focus, but don’t force it. Include the keyword and its variations in the title, opening paragraph, meta-description and throughout the body of the text (within reason).