Hello, I'm an end user like you. Is the doorbell brand new? Or is it used and about how old is it?
Assuming it is new did you fully charge the doorbell overnight first? If it is brand new then it sounds like it might be defective and I would return it to where I got it and exchange it for another one. That might just be the fastest (and least painful) way of getting up and running.
You can also try opening an official support ticket with Google. Here is the link:
https://support.google.com/googlenest/gethelp
