You just do addition but instaead of carrying the numbers over, you just write make a new digit in the number.

  1 1 
+ 1 1 
-----
  2 2

So 11 + 11 = 22

  8 8
+ 8 8
-----
 16 16

So 88 + 88 = 1616

You need to click on TRAIN button, and you will be presented with a kata trainer view and two panels of main interest:

• Solution editor is the place which contains some stub with method signature, and you need to fill it in with your solution. Solution is just a function, with arguents and return value, which is later called by tests.
• Sample tests editor which contains some test cases. This is how numbers are passed to your solution, your solution gets invoked by them, and they receive the result returned by your solution. You can add more test cases here if you want
• When sample tests pass and you believe your solution is ready, you can press ATTEMPT to test it against full, hidden test suite.

Well, if you hit the 'Train' button, you should be able to write code on the right side, and at bottom right you'll see a few testcases. (relevant link)

You will receive numbers as function arguments, and your goal is to write that function and RETURN the result.

You will complete it once you hit the 'Attempt' button and pass all test cases.

Does that make it any clearer?