Search engine optimization (SEO) is the practice of increasing the quantity and quality of traffic to your website through organic search engine results.
It used to be that you just build your website and you would be in the running for clients looking for whatever you were offering them. But since there are now so many companies offering the same thing this has become a lot harder to do, especially if you have not put the relevant information on each page for the products you wish to offer.
SEO takes time to build links and reputation to get you to the first page. The quickest way to do this is obviously by paying for digital marketing, but this becomes costly and is never ending.
Though SEO is a slow process you organic results will eventually cost you nothing, just a bit of up keep every few months to make sure everything is still good.