What happens when a creature with flying blocks my non-flying attacker?
It's your turn and you are attacking your opponent; that means you won't lose life from combat damage. The flying creature will deal combat damage to your non-flying creature. The fact that it has flying has nothing to do with it; that just determines whether it can block or be blocked.

Everything you need to know about this is covered in the basic rules; look for the section 'ATTACKING AND BLOCKING'.


  
  An attacking creature that is blocked deals damage to the creature or creatures that are blocking it, and vice versa.