As per the notes given:
"Global variables can be declared in two ways. The first is one that's already familiar to you: you just define the variable outside of any method or class, and voilà! It's global. If you want to make a variable global from inside a method or class, just start it with a $, like so: $matz."
If I am trying to do the following to create a Global Variable by defining it outside the method it doesn't work
my_variable = ""
my_variable = "Hello!"