In order to use your wearable with your Runtastic app, you need to log in to the Steps app with the same credentials as the Runtastic app (use the same account).
This way activities are already being synced to your Steps app. The wearable will also show you your current values during an activity.
In order to choose what information is being displayed on your Orbit, open the settings within your Runtastic app. On this screen, you will find the option "Runtastic Wearables“ under “App Settings”. Here you can choose what to display on your Orbit.