"After your prompt, add a switch statement that will test for several different cases (that is, different possible user inputs). Create as many as you like! (Do at least three.)"
Well, first off, a case is if the user types in a certain answer then they get "switched" to the if and else statements under that case. Basically, a chain reaction in your code to get questions and responses in this situation. The 0 in the case is the answer that the user has to type into the prompt to further prompt the switch. It is like the key to unlocking the switch. This is why a default case is so important because if no answer to the prompt matches any of your cases the code needs something to fall back on so it can still completely run. Another example of this is in my code:
var user = prompt("What is your name").toUpperCase();
console.log("That is my name too!");
If the user in the prompt answers Brad then the code will switch to the case that has Brad in it and the user will see this response on the console "That is my name too!" However, if they type in Steve, they will not get that because they did not answer with that word to switch to that particular case.
Hopefully this helps and has been at least a decent explanation. It does not go to deep in to technicallities so if you would like that I can find some articles or such that explain it a little bit more deeper or get another moderator or help desker to explain it for you.