Very easy once the supply lines to both the hot and cold water supply are shut and then work can proceed on changing out the "taps"
Usually there are no letters on French taps; some old taps bear the letters C (for chaud = hot) and F (froid = cold). Hot water taps are always located on the left side, cold water taps on the right. It is also standard to find color marks (blue for cold, red for hot) on the taps. On newer models, having a central lever instead of two taps, you turn the lever to the left for hot water and to the right for more cold water. Also the blue and red marks may be found on these type of taps.
One for hot and one for cold
No, cold water is piped into the hot water tank and is heated by electricity or gas, it then flows out to the hot water taps.
In the United States, the cold tap is usually on the right side of the faucet, and the hot tap is usually on the left side. Additionally, even though the taps may not be labelled with "hot" and "cold", sometimes the hot tap will have some sort of color marking in red, and the cold tap will have some sort of color marking in blue.
The cutoff valve from the hot water heater may have been closed.
If possible, install hammer arrestors in hot and cold water mains.
The aerator to the cold taps may be jammed, otherwise check to see that the cold water valve is switched on.
Not all plumbing devices do; some have combined hot/cold taps. In either case, hot and cold water lines are separate, the hot water coming from a water heater. The simplest taps merely control each line, letting the user measure out how much of each they want.
Mixer taps are extremely easy to use and one does not constantly have to try and get the perfect temperature and mixture of hot and cold water. Also one can make sure that hot water is not being overused.
This is personal preference and depending on your pressure. mixers need a minimum of 400kpa to function properly, or they wont work, if your pressure is below this i suggest taps. maintenance wise, mixers will last longer, however are costly to replace cartridges, where as tap washers are cheap
if someone put in a hot water tank they may have the lines switched.