Make sure that BNB is selected in the dropdown list to the right of "You send" box, and XMR is chosen in the dropdown list to the right of "You receive" box.
Enter the amount of Binance Coin Mainnet (BNB) you are going to exchange into "You send" box. Wait a couple of seconds for the recalculation to complete and check the estimated amount of Monero (XMR) in "You receive" box.
Enter the receiving XMR wallet address and, optionally, the refund BNB wallet address.
Click "Exchange" button. If all entered values are correct and valid, you will be redirected to the transaction page.
On the transaction page, copy the deposit BNB address and amount into the corresponding fields on "Send" tab/dialog box of your crypto wallet (or simply scan the QR code if you are using a mobile wallet). Send the Binance Coin Mainnet payment.
Track the status of your BNB to XMR exchange on the transaction page. Typically, most exchanges take from 5 to 60 minutes. However, in case of a crypto network congestion, the exchange process could take longer than that.
When the exchange status displays "Finished", you can check your receiving XMR wallet to make sure you have a new incoming Monero transaction.