A camera flash card will only work if it's a compact flash or SD card (all SD variants). The size can be anything you're willing to spend money on.
so then how do u put on homebrew app on the ds, can u use a SD card, and i am not willing to buy anything like a M3 or a passcard
Well for one, you'd need a media adapter. The EZIV, M3, and Supercard series of adapters are good examples of such adapters. Then, you'd need a PassMe solution. At this point, the best solutions are the nopass devices, as they are the same size as a DS game. The ones that you should consider are the Passcard3, SuperKey, MKIV, and the EZPass3.