Brawl has been out for over a year and people still dont know the difference between SDI and regular DI... You DONT need the c-stick to SDI but it helps, if you use the c stick as well as the normal joystick, its counts 2 directional inputs at the same time meaning you can SDI out of multi hit attacks faster, like snakes nair, zelda's usmash, ness' side B, etc etc... You get the idea.
SDI = Smash Directional Influence: Used during hitlag, achieved by pressing the joystick and/or cstick, moving you (more like teleporting you) with every input during hitlag. Just try it out with a smartbomb and you'll see what Im talking about.
DI = Directional Influence: Its what its called... You just push the joystick in any direction to influence the direction youre going. For example, you get hit with ness' fsmash, you want to DI up and aim for the corners in order to live longer, or DDD chaingrabs you across the stage and you know hes going to end the cg with a dtilt, you DI UP to survive, otherwise you die. One of the things that sets pros and newbies apart, pros live a lot longer because they know how to DI properly (aim for the corners).
If that's not enough for you and you'd like to learn more then read
http://www.smashboards.com/showthread.php?t=221969
Also, the controller you use is up to you... I know people who use wiichuck, people who use gc controllers and people who use the wiimote sideways (lol). Hope that helps.
At least hes trying to learn, not like you people that still think (brawls been out for over a year!) that sdi is cstick and di is joystick. Get your facts right before jumping at the guy's throat. Go read the thread I linked and educate yourselves.