First off, what about reading the DSTWO's manual!?
Nearly every game rom should save ingame; afterwards you get a "romname.SAV" file in your rom folder.
R(eal)T(time)S(ave) function has nothing to do with regular ingame saves.
It is used if you want to save while you're ingame and no savespot is near, e.g. you want to reach your bus quickly and have to shut down your DS.
RTS is available in the full hotkey DSTWO menu and does let you save the current gamestate from there. Zero means 0 RTS saveslots, three means 3 RTS saveslots for your rom and again, it has nothing to do with the game's saveslots ingame.