SEO in simple terms
SEO means "Search Engine Optimization" — the set of techniques that make your website appear higher on Google when someone searches for your services.
When someone in the US types "web design agency for small business," Google shows a list of results. Companies on that list get clients. Those not on the list don't.
Every day without SEO is a day your competition is attracting clients that could be yours. SEO is cumulative — results grow over time. Those who start earlier carry an advantage that becomes increasingly difficult to overcome.