Prepositions for location/direction

[loudasthesun.livejournal.com]

Hi,

I'm just barely starting to learn Russian, and I'm confused about the use of в/на and when to use which.

My textbook says that to state directionality (Я иду...) one uses [в/на + accusative]. Some nouns (usually "places") take в, and some nouns take на (usually "events"). There are exceptions, such as на почту. I understand this--you say "Я иду в парк", but "Я иду на стадион".

My question is... does this distinction between в/на apply to these nouns in other cases? For example, my textbook previously covered expressing location, where you use [в + prepositional], but never mentioned anything about [на + prepositional], so would these be right?

I am at the park - Я в парке
My dad works at the post office - Мой отец работает на почте
I am at a concert - Я на концерте
I am in class - Я на занятии
My mom is at work - Моя мать на работе

If I'm understanding the use of в/на + accusative/prepositional, then those above sentences should be okay. If not, can someone explain why?