Backlinks are links on other websites that link to your website. The quality and quantity of your backlinks plays a major role in improving your website in Google Search.
Beware, don’t buy backlinks. Buying backlinks can put your website at risk of Google removing it from Google Search. Typically these backlinks are on spam websites of very low quality. Black hat SEOs (unethical SEOs) try to trick Google into increasing the rank of your website by buying backlinks.