Every auction has its rules and registration procedures. Most common is that you need a deposit in form of a cashiers check usually $5000, sometimes more depending on the property price, and your pre-approval. Depending on the type of the auction the starting bid might be the lowest price that the bank will accept.
What you need to do before going to the auction is do your homework. Preview the property, the neighborhood, check the deeds, liens etc. Also check with the city/ town if there are any assessments due, check the property plot and field card. It is important that there are no issues (or small issues) with the property otherwise the bargain might turn into a financial burden.
(having an agent can help)
Best of luck