The landlords responsibilty is keeping the building safe and livable. This includes heating, plumbing, electricity, locks, walls, floors, ceilings, fire door and escapes, intercoms and elevators. Your landlord is also responsible for anything that comes with the apartment and is included in your rent such as fridge, stove, laundry facilities, furniture(if it is a furnished apartment), storage sheds and garages.
Ask the landlord for repairs in writing. Keep a copy of the letter. If you have to ask again, write another letter and keep a copy.
Keep copies of all your correspondance with your landlord. You may need copies when you move out and want your security deposit back.