When you read an English book, you often come across new words. You might try to guess what the words mean from the words you know, but when you cannot guess the meanings of new words at all, what should you do?
当你读一本英语书时，你经常会遇到生词。你可以试着从你知道的单词中猜出单词的意思，但是当你根本猜不出新词的意思时，你应该怎么做？
You have a good friend then. From him you can learn what a word means, how to pronounce a word, how to use a word, and so on. This friend can always be with you, and you can always ask him to help you. Do you know who this friend is?
你有一个好朋友。从他那里你可以学习一个词的意思，如何发音，如何使用一个词，等等。这个朋友可以永远和你在一起，你也可以永远请他帮助你。你知道这个朋友是谁吗？
It is a dictionary. You can learn some important things about words from it, so you must know how to use it.
这是一本字典。你可以从中学到一些关于单词的重要知识，所以你必须知道如何使用它。