How to make site popular without any finance? Is it even possible?

I am at high school right now. I like programming. And I have no money. I assume that's enough for my introduction.

So, today I was just having a nap and a new idea just came into my head. I googled about it and found nothing similar to my idea.

I can implement it by myself. But how can I advertise my website without any funds? Where to start? I really believe it can be useful website for a lot of people including me.

Thank you very much.