Rent a room or apartment
→ Craigslist in English
A bed for one or a few days
→ Couchsurfing Berlin
→ Hospitality club
Flat share mostly for students
→ WG Company choose ‘Help in English’ from left menu.
…same but only in German
→ WG Gesucht
→ Studenten-WG
→ Apartments in Berlin – Immobilienscout

Flat lease – German terms explained

BK / Betriebskosten: shared costs for house cleaning and maintenance.
Bürge – guarantor, see also Mietbürgschaft.
Haushaltsversicherung – household insurance.
Haftpflichtversicherung (privat) – personal liability insurance.
kalt / Heizung: “cold” rent -> rent labeled kalt does not incl. heating costs.
Makler: Agent acting on behalf of landlord, usually charging 3 months “cold” rent as provision (Maklerkosten) for signed flat rental contract.
Mietbürgschaft: lease guarantee, someone else guaranteeing in written form to pay the rent in case you fail to do so.
Miete: rent or lease, or the costs for that (context dependent).
Mietkaution: deposit of usually 2 or 3 monthly “cold” rents.
NK / Nebenkosten: costs for water consumption, trash.
warm / Heizung: heating -> rent labeled warm means incl. heating costs.
WG: – Wohngemeinschaft = flat share.
Wohnung: flat/apartment.
Zimmer: room.
Zwischenmiete: Temporary room rent, usually furnished & for a month or three.