How to Calculate Hamming Distance

I couldn't quite understand what was from edX  on Computation Structures about this topic  so I google searched a bit and came out with this

http://classroom.synonym.com/calculate-hamming-distance-2656.html

Still I have learnt quite a bit so far from the courses at edX.  I am also trying out the Discrete Time Signals course from Rice University   which seems to be a bit more comprehensible so far. Update: apart from the Hamming distance, the MIT course has been quite comprehensive so far.