It may seem odd that in a framework that embraces "convention-over-configuration" that we tackle this topic now, but since what configuration there is typically a one off, it is best to get it out the way.
With Grails' default settings you can actually develop and application without doing any configuration whatsoever. Grails ships with an embedded container and in-memory HSQLDB meaning there isn't even a database to set-up.
However, typically you want to set-up a real database at some point and the way you do that is described in the following section.