[Vulgarism]

I have a question about Hiragana/Katakana... Since it is A, I, U, E, O, and then K..., N..., H..., S..., T..., Y..., R..., W..., and N, what would you use for something that doesn't have any of those characters... Such as "desu ka" (Just as an example)... There are Hiragana and Katakana for "Su" and "Ka," but what would you use for the "De" part?? Are there special characters for those? Or am I just learning the basic Hiragana and Katakana? Are there characters other than the ones I (sorta) listed? Thanks for any help!