"alr approved some time ago"

Below the code editor there's a Sample Tests section. You can see the basic tests there. If you want to find out the inputs of the main tests, you should System.out.println(argumentVariable) inside the function to see it.

By the way, you solution doesn't work because the input is a string, you can't subtract strings.

Usually you can write to standard output of some kind, the exact way depends on the language. For C# it's Console.WriteLine, for Java - System.out.println, console.log and similar for JavaScript etc. You can see the program output in the test output window.