Untitled

module 42adder (a,b,c,d,cin, s,c1,co);
input a,b,c,d,cin;
output s,c1,co;

<guts go here>

endmodule

// module next level up
module nextmoduleup(a,b,c,d,out);
input a,b,c,d,out;
output [2:0] out;

wire sparewire = 1'b0;

// module type, then name
42adder myAdder (a,b,c,d,sparewire , out[0], out[1], out[2]);

// same connections, different instance, connect by port names
42adder myConnectbyName(
  .a(a),
  .b(b),
  .c(c),
  .d(d),
  .cin(sparewire),
  .co(out[2]),
  .c1(out[1]),
  .s(out[0])
);

endmodule