The SF-86 and FBI Cover Sheet
The SF-86 is euphemistically called "Questionnaire for National Security Positions." Basically it's the longest job application you've ever filled out.
Here is the form [PDF]. I'll do a commentary on the key sections when I have a moment.
The Cover Sheet
The FBI cover sheet asks questions of interest to the FBI that are not included in the SF-86. Among other things, the cover sheet instructs the applicant to complete each part of the SF-86 back to age 18. Here is the form [PDF].