It's used to form adjectives that describe a lack of something.
Here are some examples:
* Homeless: Without a home
* Hopeless: Without hope
* Effortless: Without effort
* Friendless: Without friends
* Thoughtless: Without thought
* Careless: Without care
* Worthless: Without worth
It's important to note that "-less" is often used in combination with other suffixes to create more complex words, like "-fulness" or "-lessness":
* Thoughtlessness: The quality of being without thought
* Carelessness: The quality of being without care
* Worthlessness: The quality of being without worth
So, the next time you see a word ending in "-less," remember that it means something is lacking or absent.