Both Green Belt and Black Belt Training are aimed at helping you improve your business by making you a better problem solver. Many people are good a coming up with solutions to problems, but are not good at actually diagnosing the problem. Lean Six Sigma uses facts and data to diagnose the problem situation so that the solutions you devise really address the right problem!
Lean Six Sigma can certainly build on your previous experience, but also can be helpful in unfamiliar areas. Many times project leaders are not the subject matter experts, but have access to such experts, and apply Lean Six Sigma approaches to jointly solve the problem in a practical manner.