If you're not using internet marketing to market your business you should be. An online presence is crucial to helping potential clients and customer find your business - even if your business is small and local. (In 2017, one third of all mobile searches were local and local search was growing 50% faster than mobile searches overall.) Online is where the eyeballs are so that's where your business needs to be.
The SEO starter guide describes much of what your SEO will do for you. Although you don't need to know this guide well yourself if you're hiring a professional to do the work for you, it is useful to be familiar with these techniques, so that you can be aware if an SEO wants to use a technique that is not recommended or, worse, strongly discouraged.