There are two kinds of AUCTIONS:
The TRUSTEE SALE is the County Auction that the house has to go thru to clear Foreclosure: The house is almost never sold at these autions; the Bank has such a high reserve, it won't sell. If you want to compete; you have to bring CASH and bid high enough. You won't know how high, and I think you will only get one bid' (may differ).
Sometimes, you will see a sign on a corner, or an ad about an AUCTION: This is a private company auctioning off a house. Maybe a good thing, maybe not. Investigate if you're interested. Caviat Emptor!
In either case, you are buying the HOUSE, not the RIGHTS to the house.