It is a list of everyone who is seeking entry to the Armed Services as an officer along with a cover letter. Those who are coming in at the pay grade less than O-5 are sent to Sec Def and anyone who qualifies for the higher grades need congressional approval. It is literally a list that has last name, first name and last four of the social security number. It is forwarded to a personnel office at the Pentagon, where it is reviewed and I believe some sort of abbreviated background investigation may happen. After review at the personnel office of the Service involved, it is sent to the Secretary of Defense.
For those who do not believe that Sec Def sees each piece of paper, the Department of Defense Instruction 1310.02, Enclosure 3, 1 b. specifically states that the Sec Def will make all Reserve appointments (sign the scroll) and that it may not be delegated further down. This is what sometimes accounts for a hold-up. If there is a lag between one secretary leaving office and the congressional approval of the replacement, there is not mechanism that allows for a scroll to be signed in the interim.