are you referring to as how to input 3 by 3 or larger matrices on a specific software platform, e.g excel, MATLAB or R? , in that case i would suggest you to do a little reading on how matrices can be input in that particular software platform.
if your question is theoretical, that is how to write a matrix using pen and paper , you can start with any introductory book on linear algebra.
Thanks so much viera, that what am looking for, I already have knowledge on it, i just want confirm whether I'm on right track or not. thanks once again for your contribution