The purpose of optimizing your site is to increase your ranking in the search results (where does your site appear in Google results?). Major search engines rank sites according to a variety of factors that signal the site’s ability to provide info relevant for a search query.
Understanding how to create content that search engines respond to is the job of SEO professionals. There’s not a huge margin for error, either. Your business basically needs to be on the first page of the search results.
There’s a lot of competition for that first-page real estate. You’re unlikely to get there without help. This is where a professional SEO agency makes all the difference.