Once all the necessary information is gathered (discussed in a previous post), the petition and the schedules can be filled out. This is usually done by your attorney and his or her staff (note: while it is possible to file for bankruptcy without providing all the necessary information at the outset, you should consult an attorney before doing so).
The petition itself is a very short document. It includes things like your name, the chapter that you are filing under, an estimation of the amount of creditors you have, and an estimation of your assets and liabilities. It also includes any bankruptcies you filed in the last eight years.
The schedules are longer, and more complex. This is where most of the information that you gathered for your attorney will be used. For example, Schedule A will list all of your real property, Schedule B will list all of your personal property, and Schedule C will list all of the exemptions you have claimed (exemptions will be discussed at a later date). The schedules will also list all of your creditors, as well as your income and expenses. The idea is that anyone (be it a creditor, the trustee, or the court) can read your petition and schedules and get a snapshot of your financial condition.