Matrix multiplication 3x3 for loops???

[4iz0pfjN]

So basically I have to tell the user to input data and i use a for loop:
for (i=0; i< 3; i++)
cin >> p[i][0],p[i][1], p[i][2];

now for the confusing part is, what do i put in the nested for loops to multiply them and output them so it looks something like

matrix p,r1: # # #
" ",r2: " "
" " " "

thanks