1) Some verbs like ждать, хотеть, искать, просить, требовать etc can take an object both in the genitive or accusative interchangeably .
хочешь водки = хочешь водку
хочешь соку = хочешь сок
(only inanimate nouns)
Textbooks usually explain the difference in the way that the genitive is used with indefinite objects and accusative with definite ones (eg.: ждать поезд -- to wait for the train, ждать поезда -- to wait for a/any train), which is just a very aritificial explanation -- the choice between the two is intuitive and depends on a particular verb and noun (i.e. with some verbs and nouns are mostly used with the genitive and others with the accusative).
2) Preposition в refers both to a place/a stay and destination/motion: в Москве -- in Moscow, в Москву -- to Moscow.
Я нИкогда не был в Москве -- I have never been to Moscow
Я в Москве уже несколько недель -- I have been in Moscow for several weeks