Upon first creating a worgen character, you begin as human citizen of Gilneas at the same time shadowy figures are seen leaping between the rooftops. It seems worgen have come to slaughter your fellow kinsmen and in the opening quest chain you play a large part in holding back the worgen and aiding the evacuation of the city. During this time you are bitten by one of the invading worgen and can see the effects of the wound progress as you continue.
Around level 5 you finish your work of evacuating Gilneas and after a cutscene (omitted in beta since it's not yet implemented) you awaken some time later in a stockade, mad from the curse that caused your transformation. Genn Graymane, the leader of Gilneas comes to see you and orders that a final attempt be made to help you gain a grip on your humanity. Here you're fed a potion that tames the beast within and you're seen fit to be released to help your fellow refugees. Your work is only beginning...
Here are some choice screenshots from the early (still inside Gilneas) parts of the worgen starting experience:
I'm making a ton of screenshots as I play, so if you're interested in seeing more I have them uploaded on my personal site and you can view them here. I frequently add more and try to keep them somewhat organized by zone or relevance.