In BladeRunnerJS an App is a collection of Aspects, BladeSets and Libraries. Apps also contain an app.conf, which configures app wide specific settings, but don't contain any code themselves. This is because your Aspects make up the different views for your app.
To create a new app use the command
$ ./brjs create-app <app-name> <app-require-prefix>
for example:
$ ./brjs create-aspect example-app appx
This will create a new app, a default Aspect to get you started and some very basic code. The require-prefix is the prefix that every require path will have in your library. This is to make it unique across your codebase so it doesn't clash with library require prefixes.