Does anyone know how to make one object say in the background be blurred and an object in the foreground in focus? And how to then make the foreground blur and background sharpen? Is this a nodes related thing? Or animation?
The effect that you are describing is called a focus pull.
“Google that.” (P.S. that is not meant as a high-tech “rtfm.”) :no:
I thought that was called “Rac-focus”?
In Blender terms, however, it is called DOF. You accomplish by setting up a node system and adding the DOF node in between the render layer and the output.
It is a nodes animation 
You have to animate the camera z depth (focus point) target. To do this you can use an empty to track to.
“Rack focus” is another name to look-up.
The effect of having only a certain set of objects in sharp focus is generically called “depth of field (DOF),” and this is employing that as a special effect. Focal-length changes are sometimes used as well. All of this can be animated in several ways, but in practice you’ll be using a Time node in the compositor since you’ll be doing the whole thing in comp, not in render.
Here is a small tutorial that I made a month ago for someone asking the same question:
http://www.burningtoken.com/blender/blenderDefocusNodeTut.m4v