Some auctions require that you register for the auction before being able to view it.
However, if registration is not a requirement, you will see a “Watch auction” box located to the right of the auction Title. This indicated that you can watch the auction without registering for it. Please keep in mind this button is only available on select auctions and while the auction is ongoing.
If the auction is ongoing and there is no "Watch Auction" button, that means the auctioneer requires all bidders to register before they can view the auction. Click here for an article on registering for an auction.