Learn German: Die Möbel stehen im Wohnzimmer. - The furniture is in the living room.

In English, "furniture" is an uncountable singular word (you say "the furniture is"). In German, die Möbel is plural. Because it's plural, you must use the plural verb form stehen (stand/are).

Why use stehen (to stand) instead of sind (are)?

German often uses positional verbs to describe exactly how an object is located, rather than just using sein (to be). Because most furniture (like tables or shelves) rests on legs or stands upright, German uses stehen (to stand) to say where it is.

What exactly is im short for?

The word im is a contraction of the preposition in and the dative article dem (in the). It is very common in German to combine these words rather than writing in dem.

Why does das Wohnzimmer change to dem Wohnzimmer here?

The preposition in is a "two-way preposition". When you use it to describe a fixed location (answering the question "Where?"), it triggers the dative case. Because Wohnzimmer is a neuter noun, its article changes from das to dem.