can you tell me more about the supplemental claim?
You can file a Supplemental Claim if you disagree with a Board's decision and have new and relevant evidence that supports your case
Another question, let's say I go and make an appeal,  what comes next to that after reviewing my case?
Well, meanwhile in review, you don't have to do anything. That is, of course, unless you receive a VA notification, probably asking you for more information.