Add a Shortcut in OS X Finder to Any Application, File or Folder You Want
In older versions of OS X, you could simply drag any icon to the toolbar to add it . You can still do this, but as Macworld points out, you need to hold down the Command key in modern versions of OS X for it to work.
If you use a particular app frequently, or if there is one folder that you always want to access in Finder, the toolbar is a good place for a shortcut. Just find the file, application, or folder you want, press and hold the Command key, then click and drag the icon onto the Finder toolbar. You can now access it right now. This is probably most useful for something like an Automator workflow, but it really depends on you how you use it.
How to Use the Finder Window Toolbar to Save Time | Macworld