you can run the interactive shell by launching the mu editorwhich you should have downloaded when going through the setup instructions in the preface on windowsopen the start menutype "mu,and open the mu app on macosopen your applications folder and double-click mu click the new button and save an empty file as blank py when you run this blank file by clicking the run button or pressing it will open the interactive shellwhich will open as new pane that opens at the bottom of the mu editor' window you should see prompt in the interactive shell enter at the prompt to have python do some simple math the mu window should now look like this in python is called an expressionwhich is the most basic kind of programming instruction in the language expressions consist of values (such as and operators (such as +)and they can always evaluate (that isreducedown to single value that means you can use expressions anywhere in python code that you could also use value in the previous example is evaluated down to single value single value with no operators is also considered an expressionthough it evaluates only to itselfas shown here rrors re ok ay programs will crash if they contain code the computer can' understandwhich will cause python to show an error message an error message won' break your computerthoughso don' be afraid to make mistakes crash just means the program stopped running unexpectedly if you want to know more about an erroryou can search for the exact error message text online for more information you can also check out the resources at python error messages and their meanings