"Hear" means to perceive sound with your ears.
"Saying" is a noun that refers to a statement, proverb, or a well-known expression.
You can use "hear" in a sentence like this:
* "I can hear the birds singing outside."
You can use "saying" in a sentence like this:
* "There's an old saying that goes, 'Early to bed and early to rise, makes a man healthy, wealthy, and wise.'"