When creating an offer, you need to decide on the amount of profit you want to receive from your trades. In the Fiat field, select your preferred currency. In the Margin field, put your margin in percentage terms. The Trade price is the market price for 1 BTC plus your profit. The price displayed in your offer will be based on this figure.
If you want to put fiat instead of the percentage value, then mark the square and enter the amount in fiat
If you want to put mark-up only in fiat, or only in percentage terms, then by clicking on the gray area of the field, you can switch from one to another
However, you should remember that prices are dynamic and change constantly with the cryptocurrency rate.