I recommend picking up Scheme, which is a variant of Lisp that follows minimalist philosophy that specifies a small standard core accompanied by powerful tools for language extension.
Now what do you need to get started? You'll need a Scheme interpreter of course! I recommend using DrRacket, which you can get at http://www.racket-lang.org
Once you have downloaded and installed DrRacket, you open in. You'll see a split window, the bottom window is called the REPL. REPL stands for Read Eval Print Loop it is a prompt where you can run Scheme code. It is kind similar to your command line, but this one only understands Scheme =)
Before you start running any Scheme code at all, you need to make sure racket is using Scheme and not Racket (which is an own dialect of Scheme). To do this, press Ctrl + L (or Cmd + L if you're on a Mac) and click then click the option which says R5RS (it should be under the "Other" -> "Legacy Languages".
Now you are all set up! The complicated is officially over!
To make sure everything is working try this expressions in your top window, then press the Run button.
(define (square x)
(* x x))
Now type: (square 8)
In your REPL, it should give you the value 64, as 8 * 8 is 64.
Now where to go from here?
The most famous book on Scheme is called "Structure and Interpretation of Computer Programs" (SICP) and is available for free at http://mitpress.mit.edu/sicp/full-text/book/book.html
If you are not the biggest fan of reading you can watch the original course on YouTube, given by the authors of SICP. However, the videos are from 1986. So the video and sound quality is everything you would expect from something form 1986, but the content of the material is still 100% relevant.
Lisp may be an old language, but it has not aged one single day. In matter of fact, a lot of languages today (i.e. Java and C++) are moving towards the ideas of Lisp and functional programming (you may have already heard of lambda expressions).
I hope you all at least give Lisp a chance.