The direct object: Я читаю книгу

The second job a noun can do

Где? gave the noun its first new ending. Here is the second job: the noun the verb acts on – what you read, watch, buy or listen to. That form is called the accusative, and it answers the question Что?

For most words there is almost nothing to do. Only feminine nouns move: -а turns into -у, -я turns into -ю. The stress and everything before the ending stay exactly where they were.

The words that never move

A masculine noun that names a thing, and every neuter noun, look as the object exactly the way they look in the dictionary. You take them as they are and change nothing.

Что? and Где? take different letters

Both endings are a single letter, and that is exactly why they get mixed up. -е follows в or на and answers Где?; the object ending -у takes no preposition at all and answers Что?

Мы слушаем музыку и пьём воду.We are listening to music and drinking water.

Что ты покупаешь? – Я покупаю книгу.What are you buying? – I am buying a book.