If we're all humans, how are we going to RP with zombies?

You'll be the zombies too. By that I mean in your RP, you'll RP the zombies are there. Confused?

Ex.

Alexander rushed down the alleyway and turned around to see the three stranglers shuffling after him. He aimed the gun at the first's face. It was a women, who, if she was still living, would be probably about in her thirties. The bite mark was obvious on her arm, so she must have died from the fever. Poor women. He squeezed the trigger and blew the Walker's brains out. She fell to the ground as the others went around her, chasing Alexander with a need of hunger, like he is the only food source that can satisfy them.

Where do I start?

The good thing about a realism-type zombie apocalypse themed RP, is you can start anywhere you want. You've got you and the Walkers to RP with at first. and others can jump in. Dontcha worry about that.

What do you mean 'Walker'

Walker is just one of the many nicknames for zombies. Others include Geeks, Zeds, Infected, etc.