Make sure you are allowed to keep them before you buy any. Chicks are easy to take care of. If you only have a few you could probably keep them in one of those big plastic totes until they are ready to go outside. (You will want to have a coop for them when they do reach that age.) Be sure to give them fresh food and water several times each day, and clean out the brooder regularly. And they will need a heat lamp to keep them warm. Raising chicks is fun, and I hope you are allowed to have them. You will enjoy them. Good luck!
There are a lot of great books on chicken raising, but before you buy any or lay some serious guilt on your parents, find out for sure if you're allowed to keep chickens where you live. It would be very sad if you had to give them up. That being said...tell your parents you'll stay on the honor roll, clean the chicken poop and get a job to pay for the coop and feed