It is fairly simple to get started. If you have an enclosed yard you will also need to build a chicken coop, buy chicks, and provide them with food and water. Chickens do not require a rooster to lay eggs and they quietly cluck around the yard eating pests in your garden and providing fertilizer to your plants. They will eat about anything, so if you decide to buy your own city chickens, it is important that you protect your prize plants so they don't get torn to shreds! Each chicken will lay about one egg per day.
There are numerous resources to help you get started. If you live in the Puget Sound region, Seattle Tilth offers classes on how to raise chickens and is hosting a City Chickens Coop Tour in July. For those of you living in the Portland area, you can attend the Tour de Coops, also in July, where you can hear and see first hand how to become an urban chicken farmer! Personally, I would be all over this if I had a backyard of my own but for now I will tend to my patio herbs and hummingbird feeder.