How to start a job portal?

Hi IH,

Over few months I was observing lot of makers are building remote job portal. Which is great way to help people, but I was always curious to know from where and how they are adding their job list from the very first day?

There are 100 of big fish in this industry then why recruiter will post a job in a newly launch portal? I hope from the very first day no one can except decent traffic in any website. Are those newly launch website owners manually adding those job post for traffic or they are following any other methods.

I am really curious to know.