Take a couple elements in a row. Say, from the 2nd to the 4th, [1, -3, 4]. Sum them, and you get 2.

Find the largest such sum, and output it.

The maximum sum subarray problem consists in finding the maximum sum of a contiguous subsequence in an array or list of integers:

So, you have to take a part (can be all the array) which sum is the greatest. In the example, there is no way to get a value greater than 6. You can't skip values, they need to be contiguous.

I can't understand what I have to do with these numbers at all.
Test.assertEquals(maxSequence([-2, 1, -3, 4, -1, 2, 1, -5, 4]), 6)
I can see in the example that I have to start from the first 4 ([i]==3) but why would I stop at the second 1 ([i]==6) ???
What do I need after all? The sum of the numbers or the sum of the numbers between 2 specific [i]'s?
If I add the numbers I get 1.
What am I doing wrong??
Please someone make me understand this, I am thirsty for knowledge.