"Manges-tu du riz ?"
Translation:Do you eat rice?
"Mange" is used with the first person singular pronoun "I" (Je): Je mange. "Manges" is used with the second person singular pronoun "You": Tu manges
Mange is also used with third person singular. Je mange, tu manges, il/elle/on mange.
This is an example of inversion. Though from what I've heard in class this form of syntax is not as common as it used to be. Now it just sounds excessively formal.
I could have swore I used "Tu mange" in a previous lesson and it was correct. So why is "Mange-tu" incorrect?
because mange is used for the first person and third person singular. regular verbs ending in -er are conjugated je mange, (-e), tu manges (-es), il/elle/on mange (-e) for singular