German builds new nouns by joining words: schlafen + Zimmer gives Schlafzimmer (bedroom). The LAST part carries the meaning and the gender - das Zimmer, so das Schlafzimmer, das Wohnzimmer, das Badezimmer. The first part only narrows it down.
Examples
- Das Schlafzimmer ist oben.
- The bedroom is upstairs.
- Die Küche ist neben dem Wohnzimmer.
- The kitchen is next to the living room.
- Wo ist das Badezimmer?
- Where is the bathroom?
The mistake to avoid
The article never comes from the first part: die Tür, but der Haustürschlüssel, because it is a Schlüssel.
Where this fits in
Home & neighbourhood, German A1: Describe your home and its rooms, say what there is in it, and talk about the places near where you live.