You go into the building & register for a buyer number. you should receive an auction list of all items. you can go & see the different items that will be auctioned.

Take a seat, wait for the auctioneers to start they will progress through the list.

How an item is sold:
1 the auctioneer will start with a base number, usually higher than you think. And fish for bids slowly dropping the price until someone lifts their hand to signal they would pay that amount. The second bid must be above the first price and it goes to the highest bidder.

Show your number to the auctioneer and record the price & bidder number. After the auction, you can pay & pick up your treasure. Be aware that the price bid does not have the auctioneer fees which can range from flat fees to 15% of the bid so a $100 purchase becomes $115

Strategy:

Don't be the first bidder, it will show your need. Second, it helps to have a budget in mind, otherwise you could overpay as you get caught up in the excitement. I like to bid towards the end of the auction of an item as it doesn't show your desire to buy.

My experience is in farm & estate auctions, fancier auction halls may have slight variations.