I Can't Properly Calculate

Anyone out there know how to fully use a calculator?



I do most of my computations in my head--keeps my mind young--but when I do use a calculating device, I never use the GPM, MRC, M-, M+, or % buttons. I know they have to do with storing numbers and reusing later, but I never really understood that part when we were learning "Calculator" in school.

On a whim, I tried to use the "%" button today, but no matter what I did, I couldn't get it to do anything, much less percentagize.