Since this appears to be academic in nature, I will give you pieces and let you put them together yourself (please no one jump in with a full solution).

Generic double for loop

for(int i = 0; i < height; i++)

for(int j = 0; j < width; j++)

dosomething(array[i ][j];

For max and min, just set them to array[0][0] and then check each element if it is higher (or lower)

Sum should be easy, start at 0 and add them all in (hint += operator is great)

Average is just sum/count.

Let me know if you need any more help.