I have a couple sites on Google and since they sold to square space I thought I'd try to keep my stuff there. But I can't figure it out. Square space is a site builder with a GUI and I can't find anywhere to just deploy my site to them as a react app. I have found a few areas where I can add some code, but they are for specific areas of the provided templates. I've even tried to use developer mode, but it looks like you still need to follow their template rules to get anywhere.
It's been a huge headache, Google made it so easy.
You'll want to create a new firebase project, install the firebase CLI on your computer and then use the CLI to: login to firebase, select the project you created, and then using the CLI run firebase deploy wherever your code is. That should use firebase "hosting" to serve your static files.
I find Google Cloud's documentation extremely confusing (including firebase), so you're not alone on that front. Took a lot of searching & troubleshooting to finally get my setup working as I intended.