You can build a 'debug' build using:
mvn package
Or a 'production' build using:
mvn package -Dproduction
Both options will build nics.war to the webapp/target/ directory
A production build takes some extra steps to optimize the static resources like minifying the Javascript.
Each 'module' is a maven jar project. It will package any compiled Java code for that module, plus any static resources (Javascript, CSS, Images) in META-INF/resources. When these jars are included in the webapp WAR project, they Java will be executed at runtime and the static resources will be available.
Just add the module as a dependency of the webapp WAR project and add any code to bootstrap your module. This will likely include adding your module to main.js in the webapp and adding html link tags for your CSS to be included.