You can not yet withdraw Bitcoin through the oblak interface.
If you have carefully noted down your seed (shown only once when you first logged in), you can use a bitcoin wallet like Electrum to create a local wallet from that seed. That way you have full control over your oblak wallet, and you can use the Electrum user interface to send and receive coins.
Caution: make sure your primary address (see it in your dashboard) has sufficient balance if you want to make use from our subscription service.