So as a new startup founder building the product is one task, but getting first users? it seems impossible at this point since I don't know any starting point and direction

Hi mate. Just seen your post. I help people get their first 100 users. It's really cheap and gets you results. Happy to help if you're interested!

The best way is to know your users before you start building. Meaning, personally know users/businesses suffering an actual problem they would be willing to pay money for to have it solved. Then build the thing that solves it.

Successful products often come out of such a starting point.

Wherever potential users congregate.

For example, people post product announcements here all the time.