click on save new address button
Then enter the bitcoin address where you would like to send your bitcoin to.
Click the next button and you will be asked for your password or your 2 factor Auth if you have turned that on.
You only have to do this once but some people like to withdrawal to a different address every time.
If you are ok for 1 address then you only need to do this once.
Now you can send however much bitcoin you wish to withdrawal or click everything and click the green withdrawal now button.
I hope that helps. If you need any more help please don't hesitate to reach out.