• Inner dimensions must be the same
• Dimension of resulting matrix are outer most dimensions of two multiplied matrices
• Resulting elements are the dot product of the rows of first matrix with the columns of the second

Try:
>> a  = [  1 2 3; 4 5 6]
a =
        1      2      3
        4      5      6
>>  b= ones (3,3)
b =
         1      1      1
         1      1      1
         1      1      1
>>  c= a*b
c  =
          6       6       6
         15      15      15