where do i get the files need for snes and sega emulators games

ok i found on the fourms here about emulators for snes and sega for ds. i got the emulators and tested them to see if they work. from what it looks like they do. the thing is they can find the files for them. i made a folder for them. so what snes file does the snes emulator need and what sega file does the sega one need.all the sega emulator i have is the one that play sonic 1 2 3 pinball and sonic and knunkles.
i might have the wrong emulator for the sega games so all can you tell what emulator i sould have
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never mind i found it had the wrong emulator work fine no souind lol

jenesis 0.7.4 or picodriveds 0.1.7

ok well i got that the one with sound but now i am have proplems with snes. i try 2 diffrent emulators but they dont pick up the roms can some one help with that
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i still cant get the snes roms to work can some one tell what the roms file has to be and what snes emulator is gor for ds