Administrative Law Judge
Generally, when you appeal to an Administrative Law Judge (ALJ) you will receive a hearing in front of an ALJ about your situation. These proceedings are like going to court, except that the proceedings are generally informal. The idea is to impartially gather information to determine whether your impairment meets or beats the Social Security listing. A hearing in front of an ALJ is not an adversarial proceeding where you are pitted against Social Security.
If the denial that brings you to an ALJ was based on a lack of information, and you obtain concrete written documentation of that missing information, you have a right to request that the Administrative Law Judge make a "decision on the record." In this situation, the judge takes the new documentation and reviews it and makes a decision without having a new hearing. While this method can speed up the process, it should not be used unless you know exactly what it will take to get a favorable decision and are able to provide it.
It is definitely preferable to hire an attorney to assist you in front of an ALJ. Most people who appear before an Administrative Law Judge with an attorney win their case. See Hiring A Representative With An Appeal.
ALJ hearings are much more informal than a regular court proceeding. If you choose to represent yourself, you can do fine if you have adequate preparation, can articulate your situation, and don't lose your cool.
For information about hearings in front of an ALJ, see:.