Most startups wait with marketing / sales of their new product / new service until the official launch. That´s not really smart, because you could generate your first customers from day 1.
Just build a website / a landingpage with a brief description what you´re doing and what the benefits for your potential customers are, and a form where you can sign up for the official waiting list. Easy.
Best, when you launch you don’t launch with 0 interests, instead you can send a personal email to the whole waiting list with a big thank you and invitation to test your new product or service.