You're right to want to complete the homework before continuing - it sounds crazy, but banging your head against a wall before solving the problem will really help you in the long run
I don't know why your code isn't compiling; you'd have to give me some source code and the error messages to help with that. The homework you're referring to asks you to stop the player from entering the same word used to generate their prompt letters. So, if the letters are "w o m b a t" don't let them enter the word "wombat".
The text tells you that the smart solution isn't to compare against the prompt letters. The reason for this is that the prompt letters have spaces between every letter, which is painful to compare against.
So, you have two options here:
1) Creating a new set of prompt letters involves pulling a word from our dictionary. How about adding that word straight to the Used List?
2) What about storing the chosen word in a new variable, then comparing the player's against that?