Homeowner has missed 1 to 3 (typically) monthly payments. 

Day 1:  Notice of Default (NOD) is sent to the homeowner. The property owner has 30 days to bring the loan current by paying any missed payments and late fees or penalties assessed by the lender.  If the defaulting property owner fails to bring the loan current the lender will likely move forward and file a notice of trustees sale next which becomes a matter of public record.

1 month later: Notice of trustee sale is filed with the county starting the foreclosure process.  The trustee schedules a Trustee's Sale (auction) date and sends the homeowner a notice of trustee sale outlining the requirements to bring the loan current and avoid foreclosure.

90 days later: On the date of sale, trustee sells the property to the highest bidder. The sale is typically held at the county courthouse.  If the bid is lower than the required minimum bid set by the lender the property reverts back to the lender, this is referred to as a REO (real estate owned).