I once read a statistic that said that most English speakers can survive using the same 50 words over and over again. While that may be true (especially since the present simple of verbs and the infinitives of words tend to be the same word), you need a lot more vocabulary to be able to communicate effectively. But how many words are enough words? How many words does the average English student need to use to be able to express ideas and thoughts?
To give you an idea of how many words are good to know (and to reassure you that you don't need to know EVERY word in English), take a look at the link below. It's the Oxford University 3000, a list of keywords that every student needs to learn because the words are important and useful:
...keywords are both frequent and used in a variety of contexts. In addition, the list includes some very important words which happen not to be used frequently, even though they are very familiar to most users of English. These include, for example, words for parts of the body, words used in travel, and words which are useful for explaining what you mean when you do not know the exact word for something.
You can find the Oxford 3000 online at: http://tinyurl.com/2ugldca.