In one sentence, describe what the following article is about:

The school or agency that requires such a letter may have certain demands of the affidavit. For example, the letter must disclose certain information, such as your name, address, and length of residency at the present address.  Some will require that a landlord sign the letter. Some letters will require the submission of other supporting documentation. Certain agencies will ask that you attach a copy of your present lease agreement or the contract to purchase the property. More commonly, a current utility bill made out to your name would also do. Most organizations will demand that the affidavit be notarized before submission. Locate the appropriate documents you will need to submit along with your letter of residency. A few examples of supporting documents include:  Lease or purchase agreements for the current residence. Utility bills for your current residence. Old tax and payroll forms that include your address information. If the agency requires the signature of your landlord on the letter, or a letter from your landlord, contact the landlord as soon as possible. If the document must be notarized, then you and the landlord both must sign in front of the notary. Not all notaries require an appointment, but you should contact local notaries beforehand to make sure that your documents can be notarized in a timely manner.

Summary:
Understand the requirements of the letter. Collect and copy supporting documents. Discuss the affidavit with your landlord. Make an appointment with a notary.