Questions & Answers about Официант наливает чаю и приносит кусок сыру.
Why is it чаю and сыру instead of the usual genitive forms чая and сыра?
This is the 'Partitive Genitive' (or Second Genitive). For certain uncountable mass nouns like чай (tea) and сыр (cheese), Russian uses the special endings -у or -ю instead of -а or -я to mean 'some of' a quantity. You will often see this with food, drinks, and materials.
Why does наливает take the genitive чаю, but приносит takes the accusative кусок?
The verb наливать (to pour) directly takes the partitive genitive here to mean pouring 'some' of a liquid. But with приносить (to bring), the waiter is bringing a specific, countable object: a piece (кусок). So кусок is in the accusative case (which looks like the nominative here because it is inanimate), and сыру is in the genitive because it tells us what the piece is made of ('a piece of cheese').
Could I say наливает чая and кусок сыра here, or is that wrong?
Why use the imperfective verbs наливает and приносит here instead of their perfective equivalents?