If you are on a Window Device, once you connect your monitor, use they keyboard shortcut Windows Key + P to bring up the output settings. Select Extend if you want to use both monitors individually.
To change the arrangement of your screens, Right-click on your Desktop and go to Display Settings (or go to Start > Settings > System >Display)
In the Select and rearrange displays section, drag the displays so the arrangement reflects their position on your desk. If it's unclear which is which, click Identify.