Zombies confuse me.

Are they dead?  They seem to be as they die and then 'reanimate', but if they are dead, why do they need to feed?  Surely they should be more like a Golem from Terry Pratchett's Discworld series, you can give them a task and they will just keep going until they are told to stop, no need for rest or food.

Are they alive?  In later series of The Walking Dead, some people turned without being bitten.  How did this happen?  

And what causes a zombie in the first place, yes I know in the majority of books and films zombies are created by a zombie biting a human, but what created the first zombie?  Is there a secret Government task force creating viruses that could do this?

What happens if a zombie bites a vampire?  Does it become a zombie that can fly?  And if this hybrid bites a human, what does the human then become?

Can zombies cope with stairs?  Would they just climb up them or would they just fall and pile up on each other eventually creating a slope for others to climb up?

These are the questions we need answers to!