First, you need to find an establishment where goods can be exchanged for notes intended as legal tender for all debts public and private. Then, once you've done that, you need to locate the section within the store that stocks dolls, and other children's toys. Once you have selected a doll you think your niece will like, take it to a cashier, which are typically found near the front of the store, often in the same area in which you entered the establishment.
Then, you're going to need engage with one of these cashiers. Hand them the doll you've selected. Sometimes rudimentary pleasantries are exchanged. The cashier will then determine the monetary value of the doll you selected, which is often indicated on the packaging of said doll. This is important to note, as before beginning your journey towards said checkout assistant, it is often helpful to know how many notes of legal tender you'll be needing to exchange.
Once your total debt has been tallied up, it will be indicated to you by the checkout assistant your total monetary indebtedness to the establishment. At this point, you're going to need to count out the total necessary funds from your small, flat case, often kept in the back pocket of your trousers, and often also holding items such as photographs and plastic cards with lines of credit assigned to them, to be able to leave the store with your doll of choice, and hand it over the the cashier, who will then return the difference to you, if you payed more than the total price due to not having exact change.
They will also then place your item in a bag, often plastic, and hand you over a paper receipt, which indicates that you now have legal ownership of the doll in your possession. At this point you're free to leave the store.
Hope this helps.
In the short time I have been here, I have never felt the need to put an emotion after a post. This changed my opinion.