VA Form 20-0995 files a Supplemental Claim. You use it after a denial when you have new and relevant evidence that VA did not have when it made the decision. You generally have one year from the date on your decision letter to keep your original effective date, so check that date first.
VA Form 21-0781 is required when you claim PTSD or a mental health condition. It asks you to describe the event or events connected to your condition. You submit it alongside your 21-526EZ. The VA uses it to verify the stressor and connect it to your diagnosis.
VA Form 21-686c adds dependents to your VA disability benefits. If your rating is 30% or higher you may be eligible for additional compensation for a spouse, children under 18, college-age children up to 23, or dependent parents. File this as soon as your rating is decided to protect your effective date.
VA Form 10182 asks the Board of Veterans Appeals to review your case. You use it when a Higher Level Review or Supplemental Claim did not resolve your denial. You have one year from your decision letter to file. There are three lanes to choose from and you can only pick one.