Thanks, that was helpful. So if I disagree with a decision of the board, I can contest it, right?
Yes, if you have new and relevant evidence that supports your case, you can file a Supplemental Claim. You can also appeal to the U.S. Court of Appeals for Veterans Claims.
What do I need to consider if I want to present new evidence?
For more information on this, you can download VA Form 20 - 0995: Supplemental Claim PDF.