To withdraw coins from your account you have to be a verified user, which means that you must provide some information as proof of your identity.
The withdrawal process itself is easy. Just go to Balance->Withdraw and find the coin name you wish to transfer, or click 'Withdraw' button next to your coin in the "Balance" tab.
Now you have to provide the address where you want to receive your coins and the amount you wish to send. Please remember that blockchain transactions are irreversible so coins sent to the wrong address cannot be recovered.
The withdrawal process should be instant, but occasionally may take some time to process. It depends on the coin you want to withdraw.
You can also check the "Fees' tab to find out what the minimum amount you are allowed to withdraw and what the fees are.