Congratulations on your new bird. Do you know if she was hand fed or is she already tame? Is she a young bird? If she has never been tamed at all, you are going to need some help. A wild cockatiel is very hard to tame, especially for a novice. If she was tame at the pet shop, then she just needs some time to get used to her new home and used to you. You can start with just talking softly to her when you give her food and water and clean her cage. You can hang out in the same room and talk to her, without trying to handle her. Wait until she shows some interest in you before you try to handle her again. Meanwhile, you should do some reading about pet birds and how to understand them. Please go to the link I provide and read the articles on that page. This will help you know how to work with her.
Caring For Your Bird