Something has been changed since I added my last application to Fabric because I just can't find how to add a new one. I made this: Settings -> Apps -> Add. The last step redirects me to the Kits page where I don't know how to continue.
Paul from Fabric here. To install a new app, choose the Crashlytics kit and follow the instructions there.
For iOS: https://fabric.io/kits/ios/crashlytics/install
For Android: https://fabric.io/kits/android/crashlytics/install