I suggest you start with a simple example, like
signal1 = zeros(1, 10);
signal1(5) = 1;
signal2 = zeros(1, 10);
signal2(8) = 1;
Then look at the length of the output and where the max/peak/spike is located. You'll figure it out.
By the way, I don't think it's well known that the max of the correlation is not always when the two signals are optimally overlapped - it just tells you when the area under the curve of the multiplication of the two signals is greatest. I believe this is why normalized cross correlation was invented. This is done by the function normxcorr2 in the Image Processing Toolbox. (Demo available upon request).
