Do I have to manually make a new local database for each new rails app?

Do I have to manually make a new local database for each new rails app?

Newbie question.
I set up a rails app to use postrges locally, which took me awhile.
Of course I had to fill in the database.yml file with the database
details, but I was doing that in the manner of a mechanical zombie, just
typing in what I thought would work without understanding why I was doing
it.
What I don't understand is whether the database was created with the rails
app when I executed rails new myProject, or if the database was created
independently during the postrgres installation and then connected to by
the app.
The result is that I'm not sure whether, upon creating a second app with
rails new mySecondProject, I need to go and somehow create a second
database for it to connect to, or whether it does that on its own and the
info I put in the database.yml file is just to give it access to my
local.....postgres program....or something like that.
Is this making sense??