Buy It Now would be used if you are selling spots to a party or event for a set dollar amount. Example $25 each spot. In this case, do not fill in the Starting Bid field and leave it blank. You will only enter the price into the Buy It Now field.
Blind Bidding would be used if you have multiple qty available for the item and you want to "Top Number" of bidders to win. Example would be with a qty of 2. The top 2 bids would win the item. Since the item is Blind Bid, the bidders will not know what the current top bids are and will be forced to put in their max bid to try and get into the top 2 spots. Any bids that are not high enough, will be notified to raise their bid. Anyone that is outbid will receive an out bid notification.