What can I do to be able to contribute to the forum?
Knowledge and expertise can be a form of contribution. If neither of these are with you, then more silence and more reading is a great initial contribution step.
Is it by reporting fraud, cheating, plagiarism or do I have to make a good post so I can be called "your contribution is great on the forum". I read a lot of posts suggesting contributing to the forum and making good posts.
That's fine as long as you can make sure you're up to the community's standards. However, basically forums need contributors to carry useful information