Listen to the whole passage
Listen to the whole passage once first, then practice sentence by sentence.
The first line is the other person opening the conversation; the "You" lines are suggestions for you to practice saying in this scenario (not a back-and-forth dialogue).
A post office clerk
你好，请问你要做什么？
Hello, may I ask what you'd like to do?
You
你好，我想寄一本书。
Hello, I'd like to send a book.
You
这本书是寄给我朋友的。
This book is for my friend.
You
请问，寄这本书多少钱？
Excuse me, how much to send this book?
You
几天能到？
How many days until it arrives?
You
这是二十块钱。
Here is twenty yuan.
You
好的，谢谢你，再见！
Alright, thank you, goodbye!