There are many applications for Nickel. For the most part it is used to cover metal surfaces that require protection from the elements. Nickel is far too expensive and hard to mine and plus it is very rare. We have to use standard metals such as Steel, Copper and Iron. To stop them from rusting we apply a coating of Nickel via the PTFE Coating process that is available from https://www.poeton.co.uk/standard-treatments/electroless-nickel-ptfe. Once this is done it affords the metal with a protective coating that will stop it, or delay it, from being exposed to the elements and rusting or tarnishing.
For the most part this is applied to metal that needs to stay strong and get a lot of use. For example hinges, screw bolts and radiator pipes. However there is one use for nickel that does not have such an industrial use.
It is the strings in an electric guitar. A standard electric guitar has six strings (unless your Steve Vai who has seven) and the bass which has four. They are made from Nickel for exactly the same reason as the hinges, to stop them from being tarnished. Strings have fingers that pull, slide and pick them. Humans secrete moisture..