Two different things decide whether a page does well: what your own page actually says, and what the rest of the internet says about it. This page covers both.
Search intent
Search intent means what a person is really hoping to find when they type a search: to learn something, to find one specific website, or to buy something. A page that answers what the searcher actually wants tends to do well. A page that just happens to use the same words, but answers a different question, does not.
Keyword research
Keyword research means finding out the exact words and phrases people really type into a search engine, so you can write about what people are actually searching for — not just the words you assume they use.
Content quality
Writing that is clear, complete, and genuinely useful tends to do better than writing that just repeats keywords over and over. Google talks about a quality idea called E-E-A-T, short for Experience, Expertise, Authoritativeness, and Trustworthiness — in plain words: does this page seem to know what it's talking about, and can it be trusted?
Off-page SEO: backlinks
Everything above happens on your own page. A backlink works differently: it is a link from someone else's website pointing to your page. When other trusted sites link to you, it works like a recommendation — a signal that your page might be worth trusting too. Because this happens outside your own site, it is called "off-page."
A note on timing
Changing a page does not change search results right away. It can take anywhere from a few days to a few weeks before you see the effect of a change.