Ordinarily in the situation that you have written about you serve and record a notice of default upon the security for the loan where the borrower gets a copy of the notice.The borrower has a certain period to cure the default and if not a notice of trustee's sale is served and recorded on the property as well where there is an auction date subject to public bid and where you have a credit bid on what is owed you. I suggest that you consult with a real estate attorney and a title company to guide you through the complicated process.