Please note that this is not a homework site. We won't do your homework for you. The purpose of homework is that you learn by doing. However we are always willing to help solve problems you encountered, correct mistakes you made in your code and answer your questions.
Your attempt to solve this problem yourself does not really have anything yet, so we cannot correct mistakes you didn't made and answer questions you didn't ask. To get help you should do more yourself and get real problems with something. If your problem is "I don't understand a thing", then you should go back to basics and study again.
Your instructions have quite a lot of information.
First step: write a function that reads the 20 characters from one file.