You can go to
R4 - R4 Revolution for DS--Official R4(R4DS) . I don't know the m3 site but it's made by the R4 team. Anyway, the micro SD goes in the card itself (on the R4 site you will see a picture of the card, the indent is where it goes). I recommend the R4 because it's easy to use and reliable- It comes with a Micro SD-USB card reader, you connect the Micro SD to your computer and drag and drop .nds files. You can also put on .txt files to use as e-books which you can read with Moonshell, which also supports photos music and video. Anyway, if you need anything else, just ask.
peace
P.S.
Also supports soft resetting ingame, pressing LRABXY ingame to return to the game menu (It can be deactivated), custom themes, cheats, etc.