mechanics question

I have a bunch of questions:

1. Does +magic dmg bonus on a weapon really work? It's not reflected in the character details.
2. what's the difference between dmg reduction and armor?
3. I've seen dodge work on spells, is block the same? How do you know if you block something?
4. I've noticed that mostly only skills that say "damage depends on weapons equipped" are capable of transferring on-hit effects from weapons like +fire DOT or +stun% (volley is one of the exceptions). Can anybody confirm this?

Thanks to anybody who answers.