Well, this tool is like a work of art!  Many people complain about the Smudge tool, but you should really learn to use it.  Think of it like finger painting.  What you have to play with is brush size and Opacity.  In this first example, I use a brush size of 25 with an Opacity of 70.  Left click and hold it down on the section you want to smudge/smear/push out or over.  While still holding down, move the cursor/brush.  Let go when you think you are done.

So you are working on a tutorial that calls for the Smudge tool to create a fur look on the edge of an animal image.  The trick here is to not use a very large brush size.  See how it looks when I use a Size 5 brush, 50% Opacity?

The reason I've tossed the Push Brush in with the Smudge Brush is to show that they are almost alike in result.  I think the only real difference is how it picks up more of the section you have started with and doesn't smear smooth as the Smudge tool.  It's up to you which effect you are looking for.  The biggest key in learning these two brushes is to simply sit down and play with them.