someone talk me through using keywords for seo?

Go back to Search Console a couple of months after publishing. Pages usually end up getting impressions for phrasing you never targeted - if one of those has decent numbers, give it a subheading and a paragraph of its own. That's how most pages grow past the original keyword.

One page, one main keyword, and check what already ranks for it first so you know if google wants a guide, a product page or a list. Then put it in the title, the H1 and the URL, and use it naturally early on. After that stop thinking about the exact phrase and cover the related questions people have around it - that does more than repeating it. The mistake that catches people is having two pages aimed at the same keyword. They end up competing with each other and neither ranks well. Merge them or give each a clearly different target.