Although most are online, the short answer is no. There are still auctions that are held live at public venues Auction.com provides details for these events on their auction calendar.
Auction.com will ask you when you are registering if you are represented by an agent. Although it is not necessary to have an agent, a professional can always help.
Once you are declared the winner of the auction, there is an earnest money deposit that is required to be paid on the day you win. Then the customer service team helps with completing contracts to send to the seller.
Some properties are going to require bidding qualifications, in this case you will be in touch with an auction.com customer service agent to guide you on specific instructions. Outside of this all you need is an internet connection and your credit card.
Once you find the property you want to bid on, click "Register for this Auction". Then you will be asked to create an account.