For example, if you are running a business website, your products are showcased in your site. Also ,many of the sites are similar like yours. How could you show or sell your product?You need to make the people to visit your website (generate more traffic to your website). Just designing and hosting your website doesn't make your site to rank in search engines.Some SEO techniques should be done to generate more traffic to your website ,also makes your website to appear in the first page of your search results.Also main thing is that create more hight quality backlinks and rank the keyword related to your product or service.
SEO categorized into two,
on-page and off-page
To know more about seo visit neilpatel,moz,backlinko,smallseo....