When describing where someone or something is, a preposition + dative is often used.

Look at the examples with in + dative:

Wo warten Nico und Max? – Im Flur. (im = in dem)
Wo kann ich Kaffee trinken? – In der Cafeteria.
Wo ist Herr Müller? – Im Büro. (im = in dem)
Wo finden die Bewerbungsgespräche statt? – In den Konferenzräumen.

Some prepositions, e.g. in, can be used with the dative as well as with the accusative. Prepositions of place with the dative are always used in answer to the question Wo …? These prepositions are known as two-case prepositions.

There are nine two-case prepositions:

in, an, unter, über, auf, vor, hinter, neben and zwischen.

Nico and Max sit in a hallway and wait. — null DW

Nico und Max warten im Flur.

An emergency exit sign on a door. — null colourbox.de

Das Schild ist an der Tür.

An empty room with two windows, there is an emergency exit sign beneath one window sill. — null colourbox.de

Das Schild ist unter dem Fenster.

A door with an emergency exit sign above it. — null colourbox.de

Das Schild ist über der Tür.

Emma sits on a chair and smiles. — null DW

Emma sitzt auf dem Stuhl.

Emma sits in front of a chair on the ground and smiles. — null DW

Emma sitzt vor dem Stuhl.

Emma stands behind a chair and smiles. — null DW

Emma steht hinter dem Stuhl.

Emma leans on the arm of a chair and smiles. — null DW

Emma steht neben dem Stuhl.

Emma stands between two chairs and smiles. — null DW

Emma steht zwischen den Stühlen.

Sometimes a short form can be made out of a preposition and an article:

in + dem = im
an + dem = am

Grammatical terms in German:

der Dativ: In German there are four different forms or categories (cases) of noun, known as Fälle or Kasus. As well as nominative and accusative, there is also dative. Nouns take this case when, for example, they come after certain prepositions or are the object of a verb that takes the dative. The articles have the forms: dem/einem, der/einer, dem/einem, den/-. In the plural an -n is often added to the noun.