When you are talking about the
location of something or somebody, or where something is happening,
you use the prepositional case to indicate the place. Statements of this kind
usually answer the question где?.
You also know that when talking about location, you use the
prepostions в or на before the noun that indicates location.
Normally, you would use the preposition в when the location is an
enclosed place. This includes cities and countries:
Письмо в портфеле.
The letter is in the briefcase.
Они живут в квартире номер 7. They live in apartment number 7.
You would use the preposition на when the location of the object,
person, or activity is on top of something:
Письмо на портфеле. The letter is on the briefcase.
На улице едут машины. Cars are driving on the street.
You also use the preposition на when the location is not really a
place, but an activity, like 'at work' (на работе), 'at a concert' (на концерте), and so on.
There are many exceptions to these rules, and they are indicated
in most dictionaries. For example, the noun завод
'factory' takes the preposition на in the prepositional.
When talking about location, Russian distinguishes between where
something or somebody is located, and the place toward which
something or someone is moving.
In English we sometimes make this distinction by using the
preposition 'at' to indicate location, and 'to' to indicate
She was at the store.
She was going to the store.
While in English you express the difference between location and
direction by using a different preposition, in Russian you use the
same preposition for both. However, when the noun indicates location it is in the
prepositional case, when it indicates direction it is in the accusative case:
Он живёт в Москве
Он едет в Москву.
Most often you will see this construction with the accusative case with verbs
of motion, or of 'going'.
You also use this construction with many other verbs that indicate
direction, such as спешить 'to hurry', and опаздывать 'to be late'.
You would use the accusative case with these verbs because they both
imply a direction toward a place.
In Russian, this construction answers the question куда? 'where