To the left pane of any Finder window sits an item called the Sidebar.  The Sidebar provides shortcuts to common locations and it is divided into two panes.

Just like most OS X interface components, you're able to customize the Sidebar to your liking.  This guide will demonstrate how you can add and remove items to and from the Sidebar.

It's easy to arrange things items in both the upper and lower pane of the the Sidebar.

It's easy to adjust the width of the Sidebar.

The Sidebar can be configured to be hidden from Finder windows.

The Finder and Sidebar co-exist in Finder Windows.  The Sidebar resides on the left side of any Finder Window.