The trading interface is composed of several components including:
Exchange / Account Context, Balances and Order Form
Ticker Bar and Chart
Account Details (Balances, Orders etc)
All these panels can be dragged around and resized to create a custom layout as desired.
To drag any panel, hover your mouse over the title area of the panel until you see the "move" icon as follows.
To resize a panel, hover your move over the lower right corner of any panel and drag to resize as desired.
If a panel appears to have disappeared below the screen, simply scroll down to find it.