There's not a lot I can say about drop C tuning other than what it is! To tune your guitar to drop C from standard tuning, you need to tune to drop D and then from there, tune down a whole step! The final result of this will be the tuning of C G C F A D. Anything played in drop D tuning, you can play in drop C tuning, it will just sound considerably more low and heavy. This tuning is becoming increasingly more common today and the lastest Metallica album, St. Anger is written almost entirely in drop C tuning!