use third party library

What steps to I have to take to use something like Mif in my app?
http://mifjs.net

Where do I have to put the source files?

script/plugin install http://github.com/creaven/miftree.git

I did that but what else do I need to do to use the library?

script/plugin install http://github.com/creaven/miftree.git

I did that but what else do I need to do to use the library?

If they are JavaScript files, you have to include them somewhere in your HTML.
The most common way is to use the javascript_tag in your layout.