No one here can help you unless you're specific with your questions. What topic in particular are you learning about? Which textbook?
None of my case studies or notes had anything about investment in them, so it's obviously specific to your topic. Try asking people who do economics for help understanding those terms if you can.
Questions in the textbook don't necessarily reflect HSC questions, and so it might not be worth getting stressed over. If you need help for an assignment then post what you need help with and I'm sure someone here will have answers for you.
Otherwise you could ask your teacher.