There is a lot of information on the forum, including examples, but basically the gross is what the players have paid, from that you have to deduct the Payment Processor Fees (around 0.5 USD + 3% per transaction, if I remember correctly). If your game has many small transactions (a very low sales value, for example 2 or 3 dollars), the percentage that the Payment Processor takes is quite high compared to the sales price.

Then you have to deduct the Itch part and if applicable, you have to consider the tax withholding and if it is the first time you make a charge to Itch, you have to pay 3 dollars to validate the tax interview.

By the way, the value you show is only an estimate, the real final value is calculated at the time of requesting the payment to Itch and there you get a spreadsheet with the detail of all the charges that apply.