Help a noob

I started my courses and am installing my shell software, but cant seem to get it to run on windows command prompt.
Im going through the steps and the youtube video provided on the second Compile and Execute course. I get all the way to step 6 on inputting the code to enable compiling, but once i do, i get the image attached. Im still getting “g++ is not recognized as an external command” message on command prompt.

Please help…