The document has three sections. Section 1 should be completed the first day the employee works for you. This establishes the identity of the employee and their knowledge of needing to provide proper documents to establish their right to work in the U.S.
In Section 2, employers verify they have viewed documents provided by employees that establishes their right to be employed. The form provides a list of acceptable documents. Never tell the employee what documents to provide; just give them the list of acceptable documents and let them decide what to provide. View original documents (no photocopies are allowed), do your best to determine their authenticity, and record all documents on the I-9. Finally, have the employee sign the document and put it in your files. This must all be completed within the first 3 days of employment for all employees regardless of citizenship status.
Section 3 of the form is used if the employee ever leaves your farm and then returns at some future date. Be sure to keep I-9 forms the appropriate length of time after an employee leaves your business. The instructions provide details.
With a little luck, you will never have to take that I-9 out for any reason other than to purge your files long after the employee has left your farm. If ICE ever questions your employees' right to work, you have the documentation to show your best efforts to determine their work eligibility. It may be tempting to keep a photocopy of the documents you were offered by the employee, but most advisors today suggest against it.
In the end, the whole thing boils down to what a rather well known comedian suggests, "Git 'er done!" You can save yourself a lot of headaches and perhaps some money as well.