This is the 12814th most frequent Russian word.
куда
"Куда" means "where to" or "to what place."
In this sentence, 'куда' is used to ask about the destination or direction of someone's movement. It means 'where' in the context of asking for a location or direction.
Куда ты идёшь?
Where are you going?
Here, 'куда' is used to inquire about the suitable location or position for placing the books. It reflects the choice of a location or direction.
Не знаю, куда положить эти книги.
I don't know where to put these books.
In this example, 'куда' is used in the context of making a decision regarding the destination of the travel or movement.