Learn Croatian: Zašto ne jedeš voće i povrće? - Why do you not eat fruit and vegetables?

In Croatian, you simply put the word ne directly before the verb to make it negative. Unlike English, which needs helper words like 'do not' or 'don't', Croatian just uses ne plus the verb. So, jedeš means 'you eat', and ne jedeš means 'you do not eat'.

Where is the word for 'you' in this sentence?

It is built right into the verb! The -š ending on jedeš tells us the subject is 'you' (singular, informal). You do not need to add the pronoun ti (you) unless you want to strongly emphasize it.

Why do voće (fruit) and povrće (vegetables) end in -e? Are they plural words?

No, grammatically they are singular. In Croatian, voće and povrće are collective nouns, meaning they describe a group of things but act like a single neuter object. The -e ending is very common for singular neuter nouns.

Do voće and povrće change their endings because they are the objects being eaten?

They are in the accusative case because they are the direct objects of the verb, but their endings do not change here. For all neuter nouns like these, the accusative (object) form looks exactly the same as the dictionary (subject) form.