Multidimensional Array

I have a text file that contains data in 20x20 array format.
I know I need to use 4 for{} loops, but I really need some help on how to do this so that I can read the entire into a 20x20 array. Also is anyone familiar with box filters? Where I have to "move" an array of 3x3 numbers over the 20x20 array to get a resultant array? I know this is a lot to ask be PLEASE HELP!

well what do you have so far?
can you declare the array?
do you know how to open and read from the file?
why 4 loops?
have you even thought about it?

If you want help then show that you have at least attempted something in code.