Quote Originally Posted by casper trumpet View Post
хорошо, у меня вопрос:
when you are saying a verb of direction(идти, бежать, лететь, etc...),
and then the preposition в or на...
how do you know which preposition to use?

for example,
идти в магазин vs идти на магазин
which one would be correct, and why?
When we speak, we don't think of prepositions, we always use the correct one automatically.
There is a correspondence:
Location у + gen. Direction к + dat. Direction from от + gen.
в + prep. в + acc. из + gen.
на + prep. на + acc. с + gen.