Stuck at Collections and Control Flow challenge 2 of 2

Below is the challenge:

This one might be a bit tricky so let's take it in steps. We have an array of numbers, nothing tricky, you've seen this before. What we want is to compute the sum of the numbers in the array. To do this we're going to use a while loop. 
We have a variable ,sum, that will store the value of the sum of numbers from the array. 
We also have a variable ,counter, which we will use to track the number of iterations of the while loop. 
Step 1: Create a while loop. The while loop should continue as long as the value of counter is less than the number of items in the array. (Hint: You can get that number by using the count property)

My first answer is OK:

while sum < numbers.count { sum++ print(numbers) }

Step 2: Now that we have the while loop set up, it's time to compute the sum! Using the value of counter as an index value, retrieve each value from the array and add it to the value of sum. 
For example: sum = sum + newValue. Or you could use the compound addition operator sum += newValue where newValue is the value retrieved from the array.

I'm lost.

let numbers = [2,8,1,16,4,3,9]
var sum = 0
var counter = 0

// Enter your code below

while sum < numbers.count {
    sum++
    print(numbers)
}