You need a flashcard. R4 is one example but I would prefer CycloDS Evolution (for ds/dslite). A flashcard is sized like a normal nds-game and has a slot for a MicroSD. You put the games on the MicroSD, put the MicroSD in the Flashcard and the flashcard in the DS. You choose a game through the menu and have fun with playing.
DS memory card? I assume you have a dsi, the memory card won't work like that, they aren't designed to. In that case you need a flash card with "i" in the name, but DO AVOID r4 brand cards if you do buy a flash cart. Like an acekard 2.i And a micro sd card to save the games to (the one's for mobiles).
