Your question is not altogether clear. If you mean that this home is being auctioned by the lender (or lenders) substitute trustees at the county courthouse, then, as other agents have wisely explained, in order to bid, you will need to follow the instructions in the newspaper published notice of foreclosure. In Fairfax County, these notices are also posted near the Courthouse entrance.
Other agents have also mentioned many of the obstacles to buying at foreclosure auctions, but the main one has just been mentioned in passing. Most lenders are required by their regulators to bid the full loan amount at auction. This is usually more than the home is worth. Otherwise, it would have sold. OK, maybe an 80/20 ( 100 - 105% financing ) situation may be an exception, but there are still condition and financing perils. I am assuming here that you are not an investor who is prepared to pay all cash for the home and who has experienced contractors available to do repairs at reasonable cost. I think you need, at the least, to engage a buyer agent to run a comprehensive series of market analyses for you to get an idea of the home's value.
There is one more real danger. Again, this has already been pointed out, but it bears repeating. There may well be other liens against the home that may not even have been filed yet, such as mechanics' liens.
I think there are so many possible troubles with buying at auction at the courthouse steps that the average home buyer would be better off buying a home that is already lender-owned.