A sell order is for selling Veritaseum, so you would sell 99 Veritaseum for each Ether in that order form by changing the amount of Veritaseum to the amount you would like to sell.
The green orders are buy orders for Veritaseum, as shown below. On these orders change the amount of Ether you would like to use or the amount of Veritaseum you would like to purchase, and click sell.
Order
Expires in 9336 blocks
Buy order: 10.000 ETH @ 25.00000 ETH/Veritaseum
Amount to sell (ETH)
10.000
Veritaseum
250.000
Fee (ETH)