Think of a product name. Buy the domain name. Launch a cloud linux server, install web server, database, application server. Configure it all up to talk to each other. Build the user creation and auth system. Implement email system for user emails. Start building the hardest bits of the application first, try to get a minimal end to end implementation of the system, iterate over the minimal version improving stuff until it’s holding together as a full application, tune, polish, do the deployment stuff.... domain name, google analytics, backups, open the firewall launch. Wonder how the fuck to get users, shut it down, build something else.