Computer Fundamentals is one of the core topics in the ITGS syllabus (that’s why it is covered in the first few chapters of the text book). Hardware, software, and networking underpin all of the examples you will ever see in ITGS (if they don’t, it isn’t an information system!), and you need to be adept at using IT terminology correctly and clearly in your exam answers.
BBC Bitesize, although designed for GCSE classes, is a good place to begin revising some computer fundamentals topics. It has revision notes and tests for several topics, including input devices, processing, and output devices (revision | test) and data storage (revision | test).
Obviously these should not be the core of your ITGS revision, but they make a good start to the computer fundamentals topics.