Many rooms are compounds of das Zimmer (room) — and a German compound takes the gender of its last part. So every -zimmer is das; the other rooms you simply learn with their article:

German	English
das Wohnzimmer	living room
das Schlafzimmer	bedroom
das Badezimmer — das Bad	bathroom
das Esszimmer	dining room
die Küche	kitchen
der Flur	hallway
der Balkon	balcony
der Garten	garden

And the things inside: der Tisch (table), der Stuhl (chair), das Sofa (sofa), das Bett (bed), der Schrank (cupboard, wardrobe), der Kühlschrank (fridge), die Dusche (shower).

The toilet is die Toilette — on signs, simply WC.