It is used to create words that have the opposite meaning of the original word.
Here are some examples:
* Non-fiction: Not fictional (meaning it is based on real events)
* Non-profit: Not seeking to make a profit (meaning it is focused on a social or charitable purpose)
* Non-toxic: Not poisonous or harmful (meaning it is safe to use)
* Non-alcoholic: Not containing alcohol (meaning it is a beverage without alcohol)
* Non-existent: Not existing (meaning it does not exist)
So, whenever you see "non-" at the beginning of a word, it generally signifies the negation or absence of the quality described by the rest of the word.