ADVICE - Any SEO expert in the room? I'm looking for some advice on where to start

Hi everybody!

This is my first time doing SEO, and I don't even know where to start. I did some google research and I understand the basic concepts (I think), but it's like it doesn't have a clear path forward. I'm recurring you, the experts, to see if you can guide me what would you recommend as first steps (and if it's possible, I don't know, what would be your next steps after those).

I built a webapp called Spendify, the easiest way of splitting tabs between friends, you only share a link and thats it. No apps, no registration. The thing is, given the B2C business model, I can't afford ads (they simply doesn't make sense, the CAC is too high), so I'm behind starting with SEO, even if that takes more time.

I really appreciate any kind of help. Leaving the link spendify.link in case you need it for your comments