Two ways to price
Against spot: a discount such as 9% below the coin's price, measured as an average over the last few minutes so a quick pump or dump can't drag your fill. Fixed: a number of SOL per coin that stays put whatever the market does.
Your price is sealed when you place the order. The program checks it at fill time, and nobody sees it before then.
Why a discount can beat the chart
Selling 3% of supply into a thin pool can cost a quarter of its value in price impact. A discount of a few percent here usually leaves the seller with more, and gives the buyer a better entry than the chart would. The dashboard works this out live for real coins under What the chart would cost.
Fee
Each fill costs 0.5%, paid by the seller out of the SOL they receive. The card shows what you get after it.