If I understand this correctly, when the government needs to raise money, they sell treasuries. The Fed holds an auction and buyers (I think mostly foreign governments) bid on these treasuries.

However, I'm pretty sure I heard (on a George Gammon podcast) that the yield of these treasuries depends on how much demand there is for them in the auction. While I know that bond prices and bond yields are inverse, what exactly are the potential buyers bidding on if they don't know what the yield will be? Are they bidding on a "10 year treasury" but don't know what the yield on that treasury is until after the auction is complete???