A few good reasons of why chickens make great pets:

Easy: Chickens are easy to keep, give them fresh water and food and they will roam and do their own thing. You don’t have to walk them multiple times a day!
Feed: Their food is cheap when compared to other animal feed and they eat scraps (Such as Vegetables, Bread, Pasta, etc).
Eggs: It’s amazing the difference between a truly fresh egg, to store bought eggs, they are much more tasty and nutritious and the yolks colour is much brighter when you crack a fresh egg. Fresh eggs also keep longer than those you get from a store because they have not spent weeks in transit.
Bugs: if you allow your chickens to roam your garden, they are a chemical free way to remove bugs. They also eat some weeds!
Poop: The poop of a chicken is a great fertilizer for plants when mixed into a composter!

Before getting your chickens the things you must obtain are:

Coop/Run: This is your chickens home, most coops these days are relatively cheap to buy, you need to consider what coop is right for your garden and right for the breed of chicken you are going to get. Most chickens like to perch but some breeds like Silkies do not like to perch too high off the ground. Once you have a coop if you don’t want a plain wooden one, you can always customize it to fit you, paint it with bright colours, add your birds name on the door, be creative!

Space: The space required depends on the size of your birds. For example 3 large fowl Cochins will need more space than 3 bantam Silkies. Allow approximately 3 large fowl hens per square metre and 4-5 Bantam hens per square metre.

Bedding: The most common bedding for chickens is pine shavings, these are great for in the main area of the coop as they are absorbent and you can scoop out any poop with ease when cleaning them out. For nesting boxes you can use pine shaving here too but some people like to use hay as its soft and the bird can build a nest for laying.

Feed: Most people feed their birds layers pellets, this has all the required nutrients for good laying. You can feed your chickens scraps as a treat (Vegetables, Bread, Pasta, etc) and also mixed corn. If your chickens are not going to be free range then they will need grit this helps digestion of food in their crop.

Feeders and Waterers: They come in various sizes which allow various quantities of feed/water. You can buy them from a poultry/farming store and some pet shops, but you can also make your own (there are many guides online).

Now that your set up its time for the fun part, picking out your birds. A lot of people these days like to keep bantam hen in their back gardens because of their small size.

Age: What age bird do you want? If you would like very tame and friendly birds its best to get younger birds and handle them regularly.

Point of lay: POL are birds that are ready to lay within a week to a month, though remember to ask the age of the birds as the bird may be in lay and be a few years old.

Hatchlings: If you want young chicks and you don’t already have a broody hen to look after them then you will need to make a brooder, this can be anything from a cardboard box to a rabbit hutch with a light in one corner so the chick can self regulate its temperature. Even young chicks enjoy outside time, if you have a small run they enjoy exploring and scratting(learning to be a chicken). Make sure they have a cover so they do not become prey to larger animals, and be sure the run is small enough that you can catch them to return to their bed.