If you look at where you assign to the variable
my_string, would you say that you are assigning a string to
my_string? There's some mention of
len on that line, what might that be doing?
Why are you printing the number 8? Shouldn't you instead be making Python count the length of the text that your variable should be refering to? You seem to have done the counting yourself. Try doing that with a book, that would take something like a second with Python, manually.. let's just not.
And which piece of text is it that you should be converting to upper case? Probably not the string literal
"my_string", it would be more useful to convert the text that
my_string refers to.