Click the calculator to use it. It should ask which of the 4 operations you wanna use. Say either division, multiplication, addition or subtraction. It then will ask which 4 numbers you want to use - say 0 for addition and subtraction if you don't need to use another number, for multiplication and division say 1.
N/A (though i suppose @Kirboys as we were making a project together then i got bored and made this)
