Hammer time and after
Keep an eye on the auctioneer and make your bids obvious but not OTT sticking your hand in the air works just fine. Try to stand where you can see how many others are bidding against you and how determined they are and don't forget that some auctions now accept online bidding.
If you've placed the winning bid, congratulations you've just bought a car. Remember, though, you won't be allowed to inspect it, then reject it, unless it has been described as having 'no major mechanical faults' or has a 'specified fault'. If so, you'll get an hour to satisfy yourself that the car is a proper runner (except for the specified fault).
Sometimes the highest bid may be 'provisional' if bidding hasn't reached the seller's reserve. The auction house will then talk to the seller to see if it can help close a deal acceptable to both parties.
You'll be expected to place a deposit straight away perhaps 10%. Most auctions will accept debit cards, then you'll need to pay the balance within a set time, and there's a buyer's fee on top. Personal cheques mean you won't be able to take the car until the funds have cleared and banker's drafts aren't much quicker. So consider a BACS electronic transaction or direct money transfer instead. Sometimes you can pay with a credit card, but a handling fee will then be added.
With your account settled, the car is yours, but you'll still need to get it home. If you intend to drive it on the road, you'll need insurance, an MoT test certificate, road tax and the correct licence plates. All of which may take time, especially if the car is sold without its V5C document, so consider hiring a transportation company with a low-loader truck.