To make a Bitcoin withdrawal you can start by pressing the 'Scan' button on the home screen. This will prompt you to scan or paste a valid Bitcoin address/Lightning invoice.
Once a valid address/invoice is scanned or pasted in, you can now choose whether to send from your BTC account or your GBP/EUR account by tapping the arrow in the middle of the screen.
For on-chain withdrawals, once you have entered the amount to send you can view different speed and fee options by tapping the 'speed:faster' button at the top. This will prompt you to select a transaction speed varying from slower to faster.
If you are not in a rush you can pay lower network fees by hitting the 'slower' button, however if you need your transaction processed quicker you can hit the 'faster' button.
You can then confirm the transaction by swiping the pay button right.
To transact on the Lightning Network you must use an external wallet that supports Lightning.
For Lightning withdrawals, once you have scanned or pasted in a valid invoice and chosen which account to pay from you can simply swipe the payment button right to confirm the transaction.
This will settle the payment instantly and for an extremely low fee compared to an on-chain transaction.