There are lot of videos/tutorials out there on youtube, udemy etc but let me summarize what is needed to build a SAAS Web App assuming you don't know anything about web apps.<p>1. Fundamentals of Web including protocols (http/https), GET/POST requests etc.<p>2. Knowledge of HTML/CSS/Javascript to build based websites/web pages.<p>3. Learning a server side language such as PHP, Python, JS/NodeJS, Go etc.<p>3. Databases and how they work with web apps. Learn SQL and database design as well. How would you create Single Tenant vs Multi Tenant apps etc.<p>4. Basic Server knowledge to host web apps. I highly recommend learning Linux Fundamentals. Also learn how to host web apps using servers such as Apache/Nginx etc.<p>5. After these 4 steps, it then comes down to picking a all-in-one mature web framework (Django for Python, Laravel for PHP etc) to build a boring monolith app OR go cooler with newer technologies, micro services, SPA, shiny new frontend framework (React, Vue, Svelte etc) and more.<p>I doubt any single source can teach you everything so the trick is to find resources on each topic as you go along. Most importantly, create something and learn every day.