Once you have saved a lot as a Favourite, it will show below.
You can then place a bid on that lot. Simply enter the amount you wish to bid and add it to your 'bid basket'.
Your Provisional Bid will appear in your bid basket, right. From there, tick the Conditions of Sale box and click 'Commit Bid'. Once your bid is confirmed, it will move into the Bids page (and disappear from your Favourites).
You can also bid from within a Lot page.