to run the circuit, enable the clock and add a number from 1 to 31 as i/p to the counter

This circuit determines whether the [Σ(Ai*Bi) for i = 0 -> i = n-1] is modulo2. 

Ai, Bi are 2-bit binary numbers and n = 32. 

The circuit stores the LSB of the final sum (when the counter reaches 31),  in a D-FF. 

If the LSB is 0 then the final sum is 0mod2 else it is 1mod2. 

The circuit is equivalant to detecting whether the sum is odd or even in decimal, given its binary form.

It remains to find how to display all the A, B pairs stored in ram, or to accept A, B pairs from the user