The Switcher is essentially the other half of the taskbar in Windows 8.
It auto-hides on the left side of the screen. Like the Charms bar on the right, you have to move your mouse cursor to the top or bottom corner and then move it towards the center in order to see the full contents of the Switcher.
If you are on the Start screen with no apps open, the Switcher does not appear at all and the left-side hot corners do nothing. If you only have one application open, the Switcher won't appear like a dock. Instead, the hot corners take you back to the app from the Start screen, while the bottom-left corner takes you back to the Start screen from the app.
You need to have two or more apps open for the Switcher to start acting like a proper taskbar.
Oddly, when you have so many apps open that you run out of space on the Switcher, apps start disappearing. They don't get smaller, and the list doesn't scroll. They're simply not listed anymore. What's more, according to the Task Manager these apps are still running, but there is nothing to indicate as much. This appears to simply be a list of the most recently launched apps, with the number of apps on the list depending on your vertical resolution.
Right-clicking on an app in the Switcher reveals a pop-up menu with the option to close that app. If you're already employing Snap, the options to Snap left or right also appear in the right-click menu.
Snapping via the Switcher's right-click menu always manipulates the sidebar app and leaves the main app alone. In other words, the main app is sticky.
As an example, let's say you have the desktop open as the main app on the left side of the screen, and Bing Weather open as the sidebar app on the right...
...but now you want to look at the News app in a sidebar on the left side of the desktop. Right-click on News in the Switcher and choose Snap left. This causes the desktop to slide right, moving the Bing Weather app off-screen and creating room for the News app on the left.
Alternatively, if you simply want to replace the Bing Weather app on the right side of the screen, choose Snap right on the News app and it replaces the Weather app.