"Confirming" status indicates that your transaction has been detected, but that we are still waiting for cryptocurrency network confirmation of the payment.
Once you see this status, there is nothing else you need to do. Feel free to close the invoice tab (though we recommend bookmarking it first), and expect an email from your seller once the payment is processed by them.
Transaction confirmation times depend on 1) the fee that was attached to the transaction and 2) the load of the cryptocurrency network. Typically, transactions confirm within an hour, but can take up to several hours or even days if the fee attached is too small.