CodeWars "12 days of Christmas"

Is it just me or is this task somewhat ambiguous with the code it’s started off with?

var comparator = function(a,b) {
  // Your code here
  return 0

I’m probably being slow but what are the inputs “a” and “b” meant to be? Two consecutive lines from the shuffled up verse?

Furthermore, the kata sets the task or rearranging the lines. The solution in the video here passes but all it seems to do is check if they’re in place to begin with? He’s not rearranging anything?

I think it would help if you research how a comparator function works first. Then, it will make sense what a and b represent and also what the function should actually return.