Ok here we go:

1. Declare the DatabaseReference object in your class, I use the lateinit modifier because it allows me declare the object without having to initialize it immediately. I can initialize it later at my leisure:

lateinit var databaseRef: databaseReference

2 I initialize it within my onCreate like so:

databaseRef = FirebaseDatabase.getInstance().getReference()

Please make sure you import 

import com.google.firebase.database.*

3 I call a method getGreeting()

 In this method I call the entry "greeting" in my Firebase app account. greeting is just a name value entry with a string as the value. To listen for the response of my call, I have the ValueEventListener added to the reference call like so:

databaseRef.child("greeting").addValueEventListener(object:ValueEventListener{

      override fun onDataChange(snapshot: DataSnapshot){\

          println("TestBed: ${snapshot.value}")

              }

       })

}

That's it really, the code below shows you the complete business

import com.google.firebase.database.*

class TestBedScrollingActivity : AppCompatActivity() {
    lateinit var databaseRef: DatabaseReference    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_test_bed_scrolling)
        val toolbar = findViewById(R.id.toolbar) as Toolbar        setSupportActionBar(toolbar)

        val fab = findViewById(R.id.fab) as FloatingActionButton        fab.setOnClickListener { view ->            Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                    .setAction("Action", null).show()
        }        databaseRef = FirebaseDatabase.getInstance().getReference()
        getGreeting()
    }
// [  Begin get greeting form Firebase  ]    fun getGreeting(){
    println("--------- start greeting ----------")
        databaseRef.child("greeting").addValueEventListener(object : ValueEventListener {

            override fun onDataChange(snapshot: DataSnapshot) {
                println("TestBed: ${snapshot.value}")
            }

            override fun onCancelled(error: DatabaseError) {}
        })
    }
//   [ End get greeting from Firebase ]