Most of the buttons are used for "programming" the calculator. You will learn about the purpose of some of these buttons in this handout. For now, ignore all the buttons to the right of the numbers. You will learn about these later in the semester.
The row of buttons at the bottom of the button area controls the calculator's activity. The buttons are "Do It", "Start", "Once/Many", "Stop", and "Reset". "Do It" is used to execute a particular command, and "Start" executes a whole sequence of commands. Pushing "Stop' while the calculator is executing a sequence of commands makes it stop, and "Reset" tells the calculator that you are ready to start all over from the first command.
"Once/Many" is used differently. It appears as "Once" but if you press it (by clicking on it), it will appear as "Many'. You can go back and forth between "Once" and "Many" by repeatedly clicking that button. The "Once/Many" button determines what happens after you have pressed "Start" and the calculator has finished all its commands. If the button appears as "Once" then the calculator simply stops. If the button appears as "Many' then the calculator starts over at the first command. This feature allows the calculator to do repeated calculations, such as encrypting each block of a long cleartext.