Here's a breakdown:
* Hacen: The third person plural form of the verb "hacer" (to do)
* menos: Means "less" or "fewer"
* cosas: Means "things"
So, the phrase literally translates to "They do less things."
Here are some examples of how you might use this phrase:
* Los niños hacen menos cosas en la escuela. (The children do fewer things at school.)
* Los robots hacen menos cosas que los humanos. (Robots do fewer things than humans.)
* Hacen menos cosas porque no tienen tiempo. (They do fewer things because they don't have time.)