It is shared by many of you that "I learnt the words by heart yesterday but now I have forgotten them. I always forget what I have learned very soon." How to master words? How many words do we have to learn? English has more words than any other language, about 1 million. The average person who speaks English has a vocabulary of some 3, 000 words. The average American, ten-year-old, probably understands some 7,000 words and uses 700 different words an hour. 

Learning a language is not for the language itself but to communicate with others and to find out about the world. When we communicate with others, we need to listen, to speak, to write and to read; when we want to find out about the world, we also need to read, to write, to listen and to speak. And all these depend on the words we keep in our mind. Words are the basic things. Words are just like the bricks people use to build houses. 
How to memorize a word and use it correctly? The best way is to put it into phrases and sentences. In this way, you can know the uses of the word and learn the word more easily. When you learn a new word, try to use your rich imagination and knowledge to make the word easier for you to learn. For example, word bomb sounds like(炸弹)；and the phrase break out has several meanings: 
Fighting broke out in the prison. Certain flu has broken out in the north of China. The fire broke out in the forest seven years ago. The war broke out in 1919. 
You can find out that "break out" means to happen suddenly and forcefully. So, you see, only when you put it into sentences can you really master it. If you do so, you won't forget it; you never waste your time. Also you should knowsomething about word-formation, such as telephone, tele-meaning far away; microcomputer, micro—meaning very small; anti-Japanese, anti-meaning against. Word-formation will help you a lot. And to do more reading is the best way to stop you from forgetting those words and phrases.

Answers:

1. About 3,000 words.
2. He thinks tht learning a language is to comunicate with others and to find out about the world.
3. The best way is to put it into phrases and sentences. 
4. Do more reading.