The switch in the hall with the red light for the shower probably means that it is an electric shower. The shower is either plumbed into the cold water system and there is a heater in the shower unit (or in the ceiling just above the shower if there is no visible shower unit) that provides all the hot water for the shower or the electric shower is plumbed into both the hot and cold and the heater in the shower unit supplements the hot water as needed.
As to the hot water to the taps, you need to work out where your hot water supply usually comes from. If you have individual hot water to your flat you either have
(a) a large copper hot water tank somewhere which is either connected to an immersion heater (an electric heating unit inside the tank) or to a conventional gas fired or oil-fired boiler, or
(b) a condensing gas or oil-fired boiler which supplies hot water on demand without storing it in the big copper tank.
If you have a copper tank and immersion heater without a boiler, check that the electricity supply to the immersion tank is switched on and has not tripped the electricity fuse. If it has tripped the fuse, or the supply is on but there is no heat, you probably need a new heating unit in the tank. That's for your landlord.
If you have a boiler in the flat, check whether it is on and working. If it's a gas boiler and there is a smell of gas, call the gas board emergency line. If it's an oil-fired boiler, check it has fuel. If the landlord has left instructions, follow them. Otherwise, again contact the landlord for help.
If you don't have a copper hot water tank or a boiler, you probably have a lease which says "hot water included", in which case the hot water arrangements are outside your flat and again you need to get in contact with your landlord.
