this is a site that sells one thing a day usually..
...a woot-off is where they sell lots of different items for around a day and a half. As soon as an item sells out they immediatly go to the next item. The yellow bar shows and estimate of how many they have left.
Items could sell out anywhere from in 10 seconds to an hour...you can get amazing deals on stuff.
Every single thing you see is virtually guaranteed to be the lowest you will find anywhere