To get started visit your local outdoor shop. Go directly to the hunting section. You should find a variety of slingshots.
Start out with some slingshot that is not very expensive. I recommend any Marksman slingshot.
NOTE: Make sure
you get your parents consent before purchasing a slingshot
WARNING: A slingshot is not a toy. To be used under adult
supervision. Make sure you go through the proper saftey course first.