Chickens aren't difficult to look after, all they require is a constant supply of water and regular food. As Martyn Loach explains, you should keep an eye open for any ailments, and they'll need to be cleaned out once a week.
All you need to keep chickens in your garden is a coop or hen house and an enclosed run. The coop can be built to your own specifications, other garden buildings such as a shed can be converted and re-purposed as a coop, or most people purchase one that is either ready built or that needs assembling. A run can be an integral part of the coop's design or you can construct one using wire mesh.