I agree with Julia. на can have different meanings in both the Prep and Acc cases. Here are some of its meanings in both: "on" (literally) + Prep - Мы сидели на стене и болтали. "in" + Prep (a synonym for в, when you have to use на not в) - Мы были на работе и на уроке, хотя мы не смотрели матч на стадионе. (likewise, points of the compass take на - на севере, востоке, юге, западе) "to" + Acc (a synonym for в, when you have to use на not в) - Мы ездим на работу и на Кавказ и на почту etc... "by" + Acc (when showing a margin of difference, with a comparative construction) - я старше его на пять лет, и она моложе меня на неделю. "for" + Acc (when showing a planned activity) - я опоздал на лекцию, на самолёт... я экономлю деньги на каникулы (because something will happen then) it's also used in slang to mean something like "here you go" when passing s.one s.th, although I think the Nominative comes after (!?) - вот тебе и на! (meaning something like "well there you go!") на деньги! (here's your money!)

Книга лежит на столе. (prepositional case) Я опоздал на самолет. (accusative case) Он сосредоточился на работе (prepositional case) In fact, I can't even imagine other examples with other cases. I checked and here it is, we use preposition на only with these two cases.

We go to somewhere can be translated in two ways: "на" & "в". If you speak about the room you are going to, use "в", because you can enter it or able to go inside of it. Я иду в театр (the building that you can enter). Положи ручку в стол. (Put the pen into the drawer of the desk) If you speak about the event you are going to, use на, because you can't physically enter it. Я иду на спектакль (the event you are going to attend). Положи ручку на стол (put the pen on top of the desk). We use В when speaking of the geographic place of living, such as countries, cities, villages etc. We say on island if this is not the country name. На Гавайях, но в Великобритании. We use "на" with all the "water" words because we mean the dry part ( the beach where you may rent a room or have a stay), except when we are speaking about actually swimming in it. Я еду на море, и буду купаться в море. I am going to the beach (to the sea in Russian - на море) and I will be swimming in the sea. Where to - куда ? - accusative case Where at - где ? - prepositional case Where from - откуда ? - genitive case Where to - Куда? Я иду на работу. - accus. Where at - Где? Я нахожусь на работе. - prepos. Where from - Откуда? Я иду с работы. - gen. ( "на" is always changed to "с") Where to - Куда? Я иду в школу. - accus. Where at - Где? Я сейчас в школе. - prepos. Where from - Откуда? Я иду из школы. - gen ("в" is always changed to "из")