Press the "Mode" key on the Casio calculator until "Comp" appears on the display. "Comp" stands for computation mode and is the primary mode you will use to enter in basic formulas to get an answer.

Use the number pad and function buttons on the keypad of the Casio calculator to input the formula you want to solve. Typical problems, such as addition, subtraction, multiplication and division can be done easily by entering in the first number, the symbol for the arithmetic you wish to perform, the final number and then the "Equals" button. You can enter multiple tasks together (for example 14+6-12) to get a final answer.

Insert parentheses where needed. The Casio MS 80 line of calculators will follow the standard order of operations, meaning that multiplication and division will occur before addition and subtraction regardless of where they are in the equation you have entered. To do a multiplication or division before addition or subtraction, use parenthesis to separate these sections. For example, entering in 4+6x5 will yield a different result than entering (4+6)x5.

Press the "Exp" button to add an exponent to the number you have just entered. Press the "(-)" button to insert a negative symbol before a number you are about to enter. You can put a negative symbol before an exponent if it is needed in the calculation.

Press the decimal point button to add a decimal in a number you are entering. Press the "a b/c" button to enter in a fraction bar between two numbers, for example, entering in 2 "a b/c" 3 will be displayed as 2/3. To enter in a percentage, press the "%" button after entering in a number you want to be used as a percentage.