According to the authors of the New General Service List, you don’t need to know a lot of words to understand English. In conversation, we tends to use a very small set of words. Radio and television both contain lots of dialogue, but the language gets more sophisticated, so you need to know about 1,500 words. To understand 90% of written text requires almost twice that number of words – almost 3,000.
Even though the English language has hundreds of thousands of words, you only need to know a relatively small number to get a grasp of English. Memorize only 10 new words a day and within one year, you’ll have a very strong understanding of English in most situations.