Some of the software as a service examples are :
- You build some software that is useful to other people.
- You expose the functionality of that software via a web interface.
- Generally, you have some user account functionality: someone signs up, they have access to the software.
- Often, you charge for access to that software (generally priced in tiers, often with a free tier).
So if you have all these parts, and you have people interested, you sell it, market it as with any other business. You either pay people to do PR, or you build.it up via word-of-mouth (Hacker News, Reddit etc).
What you’re asking is a very broad question: you’re basically asking “how do I launch a business”, there are obviously some differences between an online-only software business and everything else, but this is not the best forum to ask on. This is a forum for beginner programmers and asking on a business-related forum or FB Group or whatever would likely net you a lot more useful answers.
Thanks for your generous and apt reply. Thanks for you answer, will look forward too search for my answer on other platforms. We can try to develop that kind of community here too where people talk about businesses and startups.