Linux, and thus Ubuntu by extension, has always featured the idea of workspaces, basically multiple desktops that you can switch between at will, and thus better organise your work flow through the grouping of running applications.
With the introduction of the Unity graphical shell, Ubuntu brought to us the handy Workspace Switcher view which zooms out to a level where it displays all available workspaces, with a view of what applications are currently open in each of the workspaces, thus allowing for an easy click-through to first the workspace you want to select, and then second to the application you want to use.
The keyboard shortcut to access this Workspace Switcher is super + s.
The “super” key is generally the Windows Start key, found usually at the bottom left of a keyboard (and often decorated with the Windows logo or the word “Start”). You simply hold down this key together with the “s” key, and lo and behold the workspace switcher jumps out at you.