The Impressions Bid column is displaying the amount of impressions that your specific campaign is bidding on, and that match your campaign targeting criteria.
Impressions Bid is taking into consideration many factors, including the geo-region you are targeting, the banner sizes you added to your campaign, contextual targeting, audience targeting, device targeting, and every other filter you can apply to a campaign.
The Impressions Won column is displaying the amount of Impressions Bid that you have won. This is determined largely by your bid price and your frequency cap. Naturally, you only pay for Impressions Won. The number of impressions you’ve won, over the number of impressions you’ve bid on, is known as your Win Rate (%).