It's used to create the opposite of a word, making it negative.
Here are some examples:
* Non-fiction: Not fiction (meaning real or factual)
* Non-toxic: Not toxic (meaning safe)
* Non-profit: Not for profit (meaning charitable)
* Non-existent: Not existing (meaning not real)
* Non-stop: Not stopping (meaning continuous)
By adding "non-" to a word, you essentially negate its original meaning.