What is the author's platform? It stands for you and your book, your credibility as an author. Just like a politician you have to get your book out there to make sales. You also have to get yourself out there and become visible to your readers. It a reader doesn't know you exist how can they buy your book? Social media is not enough.
All the famous authors are out there giving talks, going to conferences, speaking where ever they can to get in front of their readers. If you want to be noticed...