A backlink is a link to your site from another website. The number of different sites linking to you is the strongest measured correlation with Google rankings.
A backlink is a link to your site from another website. How many different sites link to you was the strongest single correlation with ranking in Backlinko's study of 11.8 million results. A correlation is not proof, but it is consistent with how Google says it finds pages: by following links.
Links also cannot be faked safely. Buying them or trading them for the purpose of ranking is against Google's spam policies, and Google's guide to its AI features says chasing inauthentic mentions is not as helpful as it might seem.
For a new site, the realistic sources are pages worth citing: original data, a clear answer nobody else gives, a free tool. See how long until a new site shows on Google and what affects Google rankings.