Welcome to MATLAB! One of the great things about MATLAB is that it handles matrices (and vectors) easily. I would recommend you try to avoid loops as much as you can. There is a MATLAB function diff() that does just want you need.
x = [-2 3 -4 5 -2 5 -3 10 8 9];
y = diff(x);
Of course, if your homework is specifically to write a loop to do this, then let me give you some hints (I don't want to just write the loop for you)
The basic assignment you need is something like:
y(n) = x(n+1)-x(n);
where y is the output and x the input. Now that takes the difference of elements in a particular order, the same order as diff(). If you want it the other way:
y(n) = x(n)-x(n+1);
Since MATLAB indexes from 1, you have to think about the range of your n in the for loop. You want to start at 1, but think about how far the n go grow since you are trying to access x(n+1)
