if you have a DSTwo, put the .nds file anywhere on your MicroSD card, put it into your DSTwo, launch it, browse to the installer.nds and launch it.
install the exploit. Done.
Blue card is not needed, and if you have another flashcart it's better to use it as you already know how it works.
no need to mess with a new DS flashcart firmwares, files to copy etc.
ATTENTION:
if you choose "Boot gateway" without having EmuNAND prepared to your SD card, you will still be on SysNAND!
updating sysNAND will be game over for you.
if you want to update EmuNAND, be sure to see "GW3DS" text on the settings. If you don't see this, you will update your console's real NAND, not the emulated NAND located on SD card.
there are 4 modes:
Gateway (sysNAND)
Gateway classic (sysNAND)
Gateway (EmuNAND).
Gateway Classic (EmuNAND)
if you "prepare emuNAND", it will format your SD Card.
backup everything first!
once the SD card has EmuNAND on it, it will always boot EmuNAND when you boot into gateway or classic.
it will exit EmuNAND back to sysNAND if you exit EmuNAND settings, monster hunter or Smash bros.