In addition to obtaining your medical records, Disability Determination Services (DDS) will sometimes send a questionnaire to one or more of your doctors for completion.
Since the forms are created by each state, there is no standard. In general, the forms include questions about restrictions in your ability to perform work-related tasks, social functioning, and activities in daily living (transportation, household chores, personal hygiene) -- all information that you also provide.
If you know one is coming, alert the doctor ahead of time. Ask all your medical providers to contact you should they receive an inquiry from Social Security.
Some doctors will permit your input in the completion of the forms.
If your doctor will agree to it, review the statement before it is sent to DDS. There may be symptoms the doctor didn't include or affects on your work or daily life that aren't included.
See What Your Doctor Should Include In A Report for advice on what should be included in the report and how to get it.
NOTE: If a nurse practitioner is your medical provider, try to get the report signed by a doctor.