Pony,
If you mean, "What does the clearance process include?" here's what TSA required for the airports where I have clearance:
1. Two forms of government issued ID required, both current (They prvide a list of acceptable sources);
2. Letter from the "employer" and a form where you certify as to prior arrests or convictions for several dozen possible offences.
3. Extensive background check;
4. Finger printing (on site at airport security office);
5. Passing one or two different on-line tests given on site. These are tutorials about airport security rules, followed by on-screen questions with instant feedback if you select the wrong answer. In the cases I have seen, you must pass with 100 percent or repeat until you do. These are NOT complex.
Depending on the location, the background check could take 1 to 3 weeks. Once they notify you that you are cleared, you return to have your picture taken and get the picture ID badge.
The MSC that got me cleared paid for the background check, fingerprinting and badge fee, parking while at the airport security office, and a set sum for my time. YMMV
At the airports where I am badged I get to use a separate employee screening point or go through the high priority line at the regular screening stations. In addition, I have found that when I do buy a ticket to fly, I consistently get the TSA Pre-Approval logo on the ticket, so no more taking off shoes, etc., unless I am randomly selected for "regular" screening.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.