r4 sdhc 3ds 2015 card

Hi pretty new to this , bought my girl a 3ds xl for xmas and have successfully downloaded loads of nds games onto the memory card and all working through the r4 . how do i download 3ds games and when i do what format will they need converting to to make them work? all the nds games i have at the moment i used unpacker for mac and it made them into .nds files to get them to work i really don't know why the 3ds files won't work as the ones I've tried i converted into .3ds files but when i open up the menu the games don't show in the menu?

The cart's name doesn't directly mean it is usable to play 3ds rom. It merely means it can be use on 3ds handheld to play nds rom.

that card cannot play 3ds roms.