Where and how is secp256k1 used within Bitcoin? Bitcoin is unique that is uses secp256k1 to secure it's transactions; and any cryptographic attack against this algorithm is probably going to be percieved as an attack against the bitcoin network.

Where is this algorithm used and in what manner is it used?
All of Bitcoin's public-key cryptography is done with secp256k1. Every sane transaction has at least one secp256k1 signature and at least one secp256k1 public key or public key hash (address). A complete overnight failure of ECDSA/secp256k1 is the only technical failure I can think of which could destroy Bitcoin. This is very unlikely, though.


  Bitcoin is unique that is uses secp256k to secure it's transactions


Secp256k1 is presumably used in other applications (though Bitcoin is certainly the largest). It's a standard curve published in 2000 by Certicom Research and included in OpenSSL and other crypto libraries. Satoshi didn't just make it up or anything.