multiple shaders

so i was thinking... when you use shaders the fixed functions are GONE... so you have to use multiple shaders... right? so how would that be done??? cause all i know is that it goes this way... load your "world", load your shader then every render set your shader variables(i.e. lightpos/-dir and so on), draw your world and then the light has been applied this isin big lines but if your world is already drawn, how would you apply a second shader?? it''s kind of confusing me!! ty, Fluid FX