Let's say you are going to buy some Bitcoin (BTC) for Ethereum (ETH).
Make sure that ETH is selected in the dropdown list to the right of "You send" box, and BTC is chosen in the dropdown list to the right of "You receive" box.
Enter the amount of Ethereum (ETH) you are going to exchange into "You send" box. Wait a bit for the recalculation to complete and check the estimated amount of Bitcoin (BTC) in "You receive" box.
Enter the receiving BTC wallet address and, optionally, the refund ETH 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 Ethereum 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 Ethereum payment.
Track the status of your ETH to BTC 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 Bitcoin wallet to make sure you have a new incoming BTC transaction.