According to the UK's The Guardian, the average native English speaker regularly uses about 15,000 words and understands but does not use about 30,000, while those with degrees have roughly double that.
It depends on what you mean by how to use words. One can be quite the mundane, boring, quotidian pedant - or a logodaedalus.
Grammar is the set of rules by which word form and word order are organised. Syntax is a subset of grammar in which word order and choice of words affect the subtlety or nuance of meaning. English has strict rules of grammar, but has the most flexible syntax and largest vocabulary, which means it can express a much wider range of meanings than any other language.
A foreigner might ask, "can you borrow me that book?" instead of, "will you lend me that book?" He has not yet learned how to use the vocabulary correctly - but, with a bit of a double-take, we can work out what he probably means.
Malaprop Some people who don't know the meaning of a word might misuse it. For instance, a policeman might report, "the security guards comprehended two auspicious persons," when what he meant to say was, "the security guards apprehended two suspicious persons."
How we use words also depends on our grammar. Most of us unconsciously absorb the rules of word order by the age of six. The more articulate and educated our parents were, and the earlier we learned to socialise with others and read, the better our ability to express ourselves in words.
A common error of word use is the double negative. When the singer sings, "I can't get no satisfaction," he means to say he is dissatisfied, and colloquially we understand it. But by the rules of English grammar, one negative cancels out the other, so he is always satisfied. A phrase like this could have serious consequences in law.
How often do we say, "words cannot express it," when actually the words exist in abundance and we simply don't know them?
The right word can sometimes replace a whole paragraph.
Well crafted language can invoke sense perceptions and feelings, can communicate ideas we would never have thought of, paint pictures we have never seen, or warn us of dangers. Poor language can leave us floundering, wondering what is meant by the vague terms.
This post was edited by inky at November 5, 2018 12:38 PM MST
Communication via verbal or written word is a huge part of our existence and survival. There are many words I do not know and have to use other words to find out what that one word meant. It is nice to use words properly. It is even nicer when you expound your vocabulary. It can give you the cutting edge or a little more power than your average cat.