I do not want to talk much on this and I do not want you to get used to it because it makes you a lazy and an unprofessional player. It has advantages and more disadvantages. So If you have a Piano and you have gotten used to the functions, you would have been seeing a function called the "transpose". This function will enable you to be able make you play another key on the key that you are most familiar with.
If you want to do that, if the key you want to transpose to is on the higher octave you will use the minus button, if it is on the lower octave you will use the lower button. How do you know how many times to press it, its by counting how many notes are between the two keys you are dealing with. So if you want to transpose from the key of F# to C# you would press the plus button five times and if it from C# to F# you should press the minus button five times.