Shredding is just a term used to describe playing really fast. How to do it, heh, well that's another story. But before you begin concentrating on playing fast, I'd recommend first learning about melody and getting a good ear and sense of musical taste. There are far too many shred-heads out there who can blaze through a scale but are deficient when it comes to making interesting music.
To start you off though, you might want to look into the following terms. All are techniques used that can produce fast results when practiced a lot.
Alternate picking (a must know)
Is that it? Yeah I guess... but remember what I said about taste! I've come to learn that "shredding" isn't some far-off, elusive goal, but rather something that is surprisingly easy to achieve with the right amount of practice. One day you'll realize, damn, I can play that really fast! Then the real journey begins- implementing your new-found technique into music.