defining a function out of the results of complicated procedure

Questions
,
1

During my program, I do some symbolic calculations and finally the program comes up with a final symbolic matrix.
I need to use that matrix as a function so I could evaluate the matrix for different parameters.
something like this
y = x + z;
ss[x, z] := y;
ss[1, 2]
the result of my program goes into y.
then i want to evaluate y for different x and z but it is not working.

2

Try something like this:

y := x + z;
ss[i1_, i2_] := Block[{x = i1, z = i2}, y];
ss[1, 2]