If you're using OSGi or Apache Karaf as your application server and you've already developed features XML files for grouping bundles together as a logical application; thats all cool and they work great in fabric8.
However there's not really a big need to develop them going forward; as its easier to just create a profile zip file as part of your maven build which can automatically include all your bundles for your project.
In addition the OSGi Resolver provides a great way to automatically default the correct parent profiles, features and bundles to make it easier to get your OSGi bundles deploying correctly.
In a stand alone Apache Karaf container you install configuration files (ending in .cfg) into the etc folder to configure things via OSGi Config Admin.
The fabric8 approach is similar; but rather than an etc folder on a specific containers file system, you install the file into a profile. You can think of a profile as being a virtual etc folder which can be used by many containers.
The only difference is fabric8 uses the file name pid.properties rather than pid.cfg; so just rename the file and you should be good to go.
To add the file you can either: