var my_matrix[16];
The elements of the matrix can be accessed through the array indices [0]..[15], as usual. However, unlike normal variable arrays, a transformation matrix contains values in a special format, the IEEE 32 bit floating point format. Thus, matrix elements can not be written to or read from like normal C-Script variables. They have to be converted to the IEEE floating point or the C-Script fixed format before, like this:
my_matrix[0] = float(my_value); my_value = fixed(my_matrix[0]);
The exception is the value 0, which is the same in fixed and float format.
Handling matrix operations requires some mathematical knowledge. They are not intended for beginners to games programming, and are not necessary unless for advanced shader programming.