In 3 steps
Step 1: Setup your symfony environnement
Step 2: Generate a bundle
In your symfony project, you've got two ways to init an admin bundle :
With the SensioGeneratorBundle
In a shell write :
> php app/console generate:bundle
And after go to Step 3.
With the AdminGeneratorBundle
With this command you'll build a bundle and all controllers in one time.
> php app/console admin:generate-bundle
Step 3 : Add a generator.yml on an existing bundle
You can add generator.yml on a bundle wich already exists (created by AdmingeneratorBundle or not)
> php app/console admin:generate-admin