"Who uses this map most often?"
Translation:Kto najczęściej używa tej mapy?
There is no simple answer to this question. Even we, native speakers, have trouble choosing the right case. The best advice I can give you is to learn it by heart.
There is, however, some general rule you can follow, but bear in mind that there a lot (and I mean really a lot) of exceptions to this rule. If the verb implies that the object is in your possession, you use the accusative; for example: "Mam kawę", "Piję herbatę". If the verb implies that the object is NOT in your possession, you use the genitive; for example "Nie mam kawy", "Szukam wody". As you can see, the verb "szukać" (to look for) also implies that you don't have the object you are looking for. Unfortunately, the verb "używać" is an exception. Why? I don't have the faintest idea.
This is not entirely true – actually it's like that: In positive statements, direct object is marked by accusative and in negations by genitive; in both dative is used to denote indirect object:
- „Dałem (kogo? co? accusative) prezent (komu? czemu? dative)chłopcu”.
- „Nie dałem (kogo? czego? genitive) prezentu (komu? czemu? dative)chłopcu”.
This is the basic rule of Polish sentence structure. It is overridden by: prepositions(most force specific case), some verbs which require specific case(most well known example is verbs that have meaning of absence of direct object and therefore could be seen as negated[on conceptual level] like „szukać”, „potrzebować”[you rarely 'need' something you already have in your possession], czekać[rarely used with direct object – usually takes preposition „na”] and so on) and maybe something else I forgot about. ;)
Anyway, there is no need to learn each verb separately, you just have to remember this rule and commit to memory preposition cases plus the few verb exceptions – that is enough to use correct case in 99.8% of sentences.