To do simple arithmetic click the numbers and then press the sign for addition, multiplication, subtraction, or division. You can also type in the numbers and press + for addition, - for subtraction, * for multiplication and / for division. To view the answer press the button that is an =.
To make a number negative press the button that looks like a +/-. To insert decimals press the decimal point button which looks like . when you get to the part which is less than a whole number. To clear input from Kcalc Press the button with a C on it. To group operations so they happen together use the parenthesis to make things grouped to gether for example 2*(2+3) would give the result of 10 because it would add 2 and 3 and then multiply by two.
To copy and answer out of Kcalc press control + c or edit -> copy from the menu. To paste a number into Kcalc you can press control + v or edit -> paste from the menu. To cut the text from Kcalc press control +x or edit -> cut from the menu.
If you want even more functionality of Kcalc there is also scientific mode which is acessed from settings and the scientific mode radio button. The button 1/x takes takes 1 and divides it by the number currently on the calculator also known as taking the reciprocal. x! read x factorial will take the number X you entered and multiple each number going down to 1 for example 5! would multiply 5*4*3*2*1. The x squared button will take a x*x and multiply it by itself.