The Simplicity Studio™ IDE empowers users to highly customize their working environment, which consists of various "Views" (windows, sub-windows, etc.), through the use of "Perspectives" (essentially, various named configurations of the available Views). This enables you to most efficiently arrange your workspace to fit your screen(s) and workflow. However, it can also be frustrating at first if you accidentally make unwanted changes to the workspace, especially if it isn't clear how to undo the change.
When the View you are focusing your attention on is too small to display its full content, you can double-click on the tab for that View (or simply hit CTRL+M while that View has focus) to essentially make it "full screen". All other Views in the current Perspective are minimized away, causing the View configuration to increase the available area as much as possible to see the contents of the maximized View. Simply double-click on the tab again (or hit CTRL+M) to exit full screen and return to the previous configuration of the current Perspective.
Occasionally, you can wreak real havoc on the current Perspective (OS U/I lags causes you to accidentally click-n-drag of a View far out of place; the accidental closing of a View you can't restore because you can't find it in the main menu bar; etc.). In these cases, simply right click on the current Perspective icon (located at the top right of the Studio window) and select [Reset] as depicted below:
Your current Perspective will be restored to it's last saved state. Additionally, if you customize a perspective (inadvertently or otherwise) and like the way it looks, you can choose [Save As...] from the same Perspective right-click context menu to preserve the customized current Perspective under a new name. You can then recall this Perspective just like any of the built-in Perspectives and "reset" it if/when you make inadvertent changes.
Note that these Perspective operations are also available under the [Window] group in the Studio menu bar, including a robust [Customize Perspective...] option depicted below:
For more information on editing the built-in perspectives, see the Knowledge Base article: Overwriting the default perspective.