First of all it would be helpful if you could give some more information about the problem e.g. link or quote the task, especially if you want to complain about it calling it vague and useless. Also giving the error message might be useful as well. At the very least mention the actual exercise number this belongs to or a short description of what you want it to do and what it actually does.
var newArray= ;
var newArray = [2,3.4];
var newArray = [5,6];
Here you create the same variable 3 times with different values. That is pretty pointless and rather indicates that there is a conceptual problem and not just a bug to be fixed.
I don't know, I have just been trying different combos to see what works.
That again pretty much implies that you should rather take a break and focus on the basics, because adding random
vars is not even close to help you with multidimensional array. So if this is your problem solving mechanism then you should really review your toolkit of options and to help you understand the use of var the keyword is as @mtf already mentioned: scope and you should rather take a step back and review it because there is little use advancing if you're just poking around in the dark, is it?