BSeed's sentence beginning "So sit down with your C harp..." contains everything you need to know to get started playing blues harmonica. Interestingly, many musicans such as Charlie McCoy in Nashville, Greg "Fingers" Taylor with Jimmie Buffett, Mickey Raphael with Willie Nelson, etc. use the "cross-harp" technique (C harmonica to play in the key of G, etc.) regardless of what style music they are playing (blues, country, rock, folk)­probably because, as BSeed points out, in this style drawn notes predominate, and drawn notes can be played with considerably more feeling, shaping, expressiveness and control than blown notes. Good luck! P.S. I would resist the urge to all the harmonica a harp. There is already a musical instrument bearing that name.