Hidden Power
Hidden Power is an attack that can be any type (except Normal) and any Base Power between 30 and 70. What this type and power is, is determined by your Pokemon's DVs/IVs. These are values that range between 0 and 31, and there is one allocated to every stat. They cannot be changed without cheating, and as a result each Pokemon will only ever have one Hidden Power Type and Power.
The DVs/IVs are not visible on your Pokemon; you need to know the EVs, Base Stats, level and stat of your Pokemon in order to find them. However, you shouldn't need to worry about finding them, as the easiest way to test a Pokemon's Hidden Power type is by attacking different types of Pokemon and using a weakness/resistance chart to figure out what type it is.
Hidden Power is a good move because it can teach a Pokemon a certain type of attack that it may not normally be able to learn, and can cover weaknesses accordingly (eg: Shedinja can learn HP Fighting, covering Rock and Dark weaknesses). Whether you use it or not is up to you, but it is a good attack if you have patience enough to get the right type and power.
