Download form I-9 to your computer, open pdf (in Acrobat Reader) and fill-in document add your signature (see STEP 1 FREE Adobe Account) re-name file with your name. You can submit 2 proof of documents: Drivers License and Social Security Card or Passport page containing picture.
https://www.uscis.gov/sites/default/files/document/forms/i-9-paper-version.pdf